The first three nonzero terms of two linearly independent solutions about x = 0 can be obtained by Taylor expanding the solutions in terms of the exponent r and truncating the series to the desired order.
To determine if x = 0 is a regular singular point of the differential equation xy'' + y = 0, we substitute y = x^r into the equation and solve for the exponent r. Differentiating y twice with respect to x, we have y'' = r(r - 1)x^(r - 2). Substituting these expressions into the differential equation, we get [tex]x(x^r)(r(r - 1)x^(r - 2)) + x^r = 0[/tex]. Simplifying, we obtain r(r - 1) + 1 = 0, which yields r^2 - r + 1 = 0. Solving this quadratic equation, we find that the exponents at the singular point x = 0 are complex and given by r = (1 ± i√3)/2.
To find the first three nonzero terms of two linearly independent solutions about x = 0, we can use the Taylor series expansion. Let's consider the solution y1(x) corresponding to the exponent r = (1 + i√3)/2. Expanding y1(x) as a series around x = 0, we have y1(x) =[tex]x^r = x^((1 +[/tex]i√3)/2) = x^(1/2) *[tex]x^(i√3/2[/tex]). Using the binomial series expansion and Euler's formula, we can write [tex]x^(1/2) and x^(i√3/2)[/tex] as infinite series.
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Plz help me out thanks
Answer:
the full answer is 215.859885inches cubed
Step-by-step explanation:
times the length, width and height together
Apply the properties of exponents to determine which of these numerical expressions
are equivalent to 5^12. Select all that apply.
Very confused and forgot the rules to figuring this out.
Answer:
Second One-
[tex] {5}^{14}. {5}^{ - 2} [/tex]
Fifth One-
[tex] {5}^{6} \: . \: {5}^{6} [/tex]
Sixth One-
[tex] \sqrt{ {5}^{24} } [/tex]
Seventh One-
[tex] {5}^{11} \: . \: 5 [/tex]
In a normal distribution, 95% of the data falls within 1 standard deviation of
the mean.
True or False?
Answer:
False
Step-by-step explanation:
A P E X
PLEASE PLEASE PLEASE HELP 7 points
Answer:
a) 2x+(x+36)=90
Step-by-step explanation:
b) A1+A2=90°. (A=angle)
2x+(x+36)=90
2x+x+36=90
3x+36=90
3x=90-36
x=54/3
x=18
then A1=2x=2*18=36°
A2=x+36=18+36=54°
Consider Z is the subset of R with its usual topology. Find the subspace topology for Z.[r2]
The subspace topology for Z, which is a subset of R with its usual (standard) topology, is the set of open sets in Z.
In other words, the subspace topology on Z is obtained by considering the intersection of Z with open sets in R.
To find the subspace topology for Z, we need to determine which subsets of Z are open. In the usual topology on R, an open set is a set that can be represented as a union of open intervals. Since Z is a subset of R, its open sets will be the intersection of Z with open intervals in R.
For example, let's consider the open interval (a, b) in R. The intersection of (a, b) with Z will be the set of integers between a and b (inclusive) that belong to Z. This intersection is an open set in Z.
By considering all possible open intervals in R and their intersections with Z, we can generate the collection of open sets that form the subspace topology for Z. This collection of open sets will satisfy the axioms of a topology, including the properties of openness, closure under unions, and closure under finite intersections.
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A coffee shop recently sold 8 drinks, including 2 Americanos. Considering this data, how many of the next 20 drinks sold would you expect to be Americanos?
Answer:
5 drinks will be americanos
Step-by-step explanation:
2:8 (2/8)
simplify
1:4 (1/4)
divide 20 by 4
5:20
The number of next 20 drinks which may be Americanos is 5.
What is Probability?Probability is simply the possibility of getting an event. Or in other words, we are predicting the chance of getting an event.
The value of probability will be always in the range from 0 to 1.
Given that,
Total drinks sold = 8
Number of drinks that is Americanos = 2
Probability of finding Americano = 2/8 = 1/4
If the total number of drinks next is 20,
Number of Americanos expected = Probability of Americanos × Number of drinks
= 1/4 × 20
= 5
Hence the number of Americanos expected is 5.
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Park trails and their elevation:
Sand trail has a -2 feet elevation
Cactus Trail has 15 feet elevation
Southern Trail has a -12 feet elevation
Rocky Trail has 42 feet elevation
Chi hiked the Rocky Trail What is the opposite of the elevation of the Rocky Trail?
Answer:
fjekwnkewgnelwnlgnendndj
Step-by-step explanation:
Compute the pooled variance given the following data:
N_1 = 18, n_2 = 14, s_1 = 7, s_2 = 8
Round to two decimal places
By computing the pooled variance given the following data N_1 = 18, n_2 = 14, s_1 = 7, s_2 = 8, the pooled variance is 436.40.
To compute the pooled variance given N_1 = 18, n_2 = 14, s_1 = 7, s_2 = 8, we can use the formula below;
S_p² = [(n₁ - 1)S₁² + (n₂ - 1)S₂²] / (N - 2),
where S_p² = pooled variance, n₁ = sample size of first group, n₂ = sample size of second group, S₁² = variance of first group, S₂² = variance of second group, and N = total sample size.
To plug in the values, we have: N₁ = 18n₂ = 14S₁ = 7S₂ = 8
Substituting the values into the formula above we get;
S_p² = [(18 - 1)(7²) + (14 - 1)(8²)] / (18 + 14 - 2)S_p² = (17 × 49 + 13 × 64) / 30S_p² = 436.4
Round off to two decimal places to get 436.40.
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John buys 6 shirts. For every shirt you purchase, you get one for 30% off. If the normal
price for each shirt is $20.00, how much money did John spend on his shopping trip? (Tax is not being calculated.)
Answer:
$36
Step-by-step explanation:
Basically, every shirt is $6 because 30% of 20 is 6. If he buys 6 shirts, then 6 times 6 is 36 dollars spent, tax not included.
Concession stand sales for each game in season are $320, $540, $230, $450, $280, and $580. What is the mean sales per game? Explain how you got your answer.
Answer:
$400
Step-by-step explanation:
all you do is add 320+540+230+450+280+580/6 and the asnwe comes out to 400
In real-life applications, statistics helps us analyze data to extract information about a population. In this module discussion, you will take on the role of Susan, a high school principal. She is planning on having a large movie night for the high school. She has received a lot of feedback on which movie to show and sees differences in movie preferences by gender and also by grade level. She knows if the wrong movie is shown, it could reduce event turnout by 50%. She would like to maximize the number of students who attend and would like to select a PG-rated movie based on the overall student population's movie preferences. Each student is assigned a classroom with other students in their grade. She has a spreadsheet that lists the names of each student, their classroom, and their grade. Susan knows a simple random sample would provide a good representation of the population of students at their high school, but wonders if a different method would be better. a. Describe to Susan how to take a sample of the student population that would not represent the population well. b. Describe to Susan how to take a sample of the student population that would represent the population well. c. Finally, describe the relationship of a sample to a population and classify your two samples as random, cluster, stratified, or convenience.
a. To take a sample of the student population that would not represent the population well, Susan could use a biased sampling method.
For example, she could choose students only from specific classrooms or grade levels that she believes have a certain movie preference, or she could select students based on her personal biases or preferences. This would introduce sampling bias and potentially skew the results, leading to a sample that does not accurately reflect the overall student population.b. To take a sample of the student population that would represent the population well, Susan should use a random sampling method. Random sampling ensures that every student in the population has an equal chance of being selected for the sample.c. A sample is a subset of the population that is selected for analysis to make inferences about the entire population. The relationship between a sample and a population is that the sample is used to draw conclusions or make predictions about the population as a whole.To know more about Random samples:- https://brainly.com/question/30759604
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One winter day, the temperature ranged from a high of 40 °F to a low of -5 °F. By how many degrees did the temperature change?
O 55
O 25
O 45
O 35
Answer:
45
Step-by-step explanation:
the correct choice is C.
Trigonometry question help,,, NO LINKS
Answer:
87 ft
Step-by-step explanation:
SohCahToa is your best friend here.
You have two values you need to pay attention to:
The length that is adjacent to the 74°C, 25 ft. And the length opposite of the 74°C, the height of how high the rocket traveled.
So adjacent and opposite, O & A. "Toa", find the tangent of 74°C.
tan(74) = [tex]\frac{x}{25}[/tex]
x = (tan(74))(25)
x = 87 ft
"
A Bernoulli differential equation is one of the form dy + P(x)y dx Q(x)y"" (*) Observe that, if n = 0 or 1, the Bernoulli equation is linear. For other values of n, the substitution u = yl-n
For values of n other than 0 or 1 in a Bernoulli differential equation, the substitution [tex]u = y^{(1-n)[/tex] is used to transform it into a linear equation.
A Bernoulli differential equation is given by the form:
dy + P(x)y dx = Q(x)[tex]y^n[/tex] (*)
If we consider the case when n = 0 or n = 1, the Bernoulli equation becomes linear. Let's examine each case:
When n = 0:
Substituting[tex]u = y^{(-n) }= y^{(-0)} = 1[/tex], the differential equation becomes:
[tex]dy + P(x)y dx = Q(x)y^0[/tex]
dy + P(x)y dx = Q(x)
This is a linear differential equation of the first order.
When n = 1:
Substituting [tex]u = y^{(-n) }= y^{(-1)},[/tex] we have:
[tex]u = y^{(-1)[/tex]
Taking the derivative of both sides with respect to x:
[tex]du/dx = -y^{(-2)} \times dy/dx[/tex]
Rearranging the equation:
[tex]dy/dx = -y^2\times du/dx[/tex]
Now substituting the expression for dy/dx in the original Bernoulli equation:
[tex]dy + P(x)y dx = Q(x)y^1\\-y^2 \times du/dx + P(x)y dx = Q(x)y\\-y \times du + P(x)y^3 dx = Q(x)y[/tex]
This equation is also a linear differential equation of the first order, but with the variable u instead of y.
In summary, when n is equal to 0 or 1, the Bernoulli equation becomes linear. For other values of n, a substitution u = y^(-n) is typically used to transform the Bernoulli equation into a linear differential equation, allowing for easier analysis and solution.
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Let R be a commutative ring with 1. An element x ER is nilpotent if x=0 for some n E N. (a) Prove that the set N(R) := {x ER: x is nilpotent} is an ideal of R. (b) Prove that N(R/N(R)) = 0.
(a) To prove that the set N(R) = {x ∈ R: x is nilpotent} is an ideal of the commutative ring R with 1.
We need to show that it satisfies the two conditions of being an ideal: closure under addition and closure under multiplication by elements of R.
To demonstrate closure under addition, let x and y be nilpotent elements in N(R). This means that there exist positive integers m and n such that xm = 0 and yn = 0.
We want to show that x + y is also nilpotent. By expanding (x + y)^k using the binomial theorem, we can see that each term involves a product of powers of x and y. Since both x and y are nilpotent, their product is also nilpotent.
Therefore, the sum (x + y) raised to a sufficiently high power will result in zero, showing that x + y is indeed nilpotent. Hence, N(R) is closed under addition.
To prove closure under multiplication by elements of R, let x be a nilpotent element in N(R) and r be any element in R. We aim to show that rx is nilpotent. Since x is nilpotent, there exists a positive integer m such that xm = 0.
When we raise rx to a sufficiently high power, (rx)^k, it can be expanded as r^k * x^k. Since x^k is zero due to x being nilpotent, the product r^k * x^k is also zero. Therefore, rx is nilpotent, and N(R) is closed under multiplication by elements of R.
Hence, N(R) satisfies both conditions of being an ideal, and thus, it is an ideal of the commutative ring R.
(b) To prove that N(R/N(R)) = 0, we want to show that every element in R/N(R) is not nilpotent.
Let [x] be an element in R/N(R), where [x] represents the equivalence class of x modulo N(R). Our goal is to demonstrate that [x] is not nilpotent, meaning it is not equal to the zero element in R/N(R).
Suppose, for contradiction, that [x] = 0 in R/N(R). This would imply that x belongs to N(R), the set of nilpotent elements in R. However, if x is an element of N(R), it means that x is nilpotent, and by definition, there exists some positive integer n such that xn = 0. This contradicts our assumption that [x] = 0, since it would imply that x is not nilpotent.
Therefore, our assumption that [x] = 0 leads to a contradiction, and we conclude that every element in R/N(R) is not nilpotent.
Consequently, N(R/N(R)) = 0, indicating that the set of nilpotent elements in the quotient ring R/N(R) is empty.
In summary, we have shown that N(R/N(R)) = 0 and established that N(R) is an ideal of the commutative ring R.
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PLSSS HELP IMMEDIATELY!!!!! i’ll give brainiest, i’m not giving brainiest if u leave a link tho. (pls check whole picture!!)
Answer:
(4,2)
Step-by-step explanation:
Answer:
(4, 2)
Step-by-step explanation:
What is the y-intercept for the equation y= 11x + 1?
-11
-1
1
11
Answer:
1
Step-by-step explanation:
The y-intercept in the equation is 1 because the equation uses the format y=mx+b. The b in y=mx+b represents the y-intercept So, in this equation the y-intercept is 1 because b=1.
Can someone help me ill give you 25 points!!! no wrong answers or ill have brainly take all your points and band you forever Uhm yeah so......... plz help
Answer: Mean = 2.36 Median = 4 Range = 0
Step-by-step explanation:
Mean - the sum of the data values divided by the number of data values
Median - the middle number in an ordered set of data
Range - the difference between the greatest and least numbers in a data set
what are some good editing apps i use alight motion and capcut
:))))))
Step-by-step explanation:
videochamp, picsart
Picsart , Inshot , Gandr , Photo lab and Viva video.
jesse has never used the sliding board at his daycare because he is afraid. His teacher has encouraged him, but he refuses to slide down. one day his mother stands at the bottom And say's Jesse let's go and slides into his mother's arms Laughing The situation is a example of....
A Resiliency
B Adaptability
C Conditioning
D Social referencing
jesse has never used the sliding board at his daycare because he is afraid. His teacher has encouraged him, but he refuses to slide down. one day his mother stands at the bottom And say's Jesse let's go and slides into his mother's arms Laughing The situation is a example of Social referencing. Option (d) is correct.
What do you mean by Situation?Situation refers to a group of conditions or a current state of events.
Social reference is the method through which newborns control their behavior toward surrounding items, people, and circumstances by observing the emotive displays of an adult.
For adaptive social functioning to occur, one must recognize and make use of the emotional communication of others. The ability to negotiate complicated and frequently ambiguous settings is known as social referencing in the developmental literature and social appraisal in adult studies.
Therefore, Option (d) is correct. The situation is a example of Social referencing.
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Find the absolute value of the number for point E.
Answer:
1
Step-by-step explanation:
Answer:
The answer is 1
Step-by-step explanation:
E is -1 and the absolute value is the posotive of any number. The positive of -1 is 1.
The solution to a logistic differential equation corresponding to a specific hyena population on a reserve in A western Tunisia is given by P(t)= The initial hyena population 1+ke-0.57 was 40 and the carrying capacity for the hyena population is 200. What is the value of the constant k? (A) 4 (B) 8 (C) 10 (D) 20 6. Which of the following differential equations could model the logistic growth in the graph? AM 50 40 30/ 20 10 t (A) (B) dM =(M-20)(M-50) dt dM = (20-MM-50) dt dM = 35M dt dM = 35M(1000-M) dt (C) (D)
The logistic differential equation for the hyena population is given by:
dP/dt = r * P * (1 - P/K)
where P(t) is the hyena population at time t, r is the growth rate, and K is the carrying capacity.
We are given that:
P(t) = 40 + k * e^(-0.57t)
K = 200
To determine the value of k, we can plug in these values into the logistic differential equation and solve for k:
dP/dt = r * P * (1 - P/K)
dP/dt = r * P * (1 - P/200)
dP/dt = r/200 * (200P - P^2)
dP/(200P - P^2) = r dt
Integrating both sides, we get:
-1/200 ln|200P - P^2| = rt + C
where C is a constant of integration.
Using the initial condition P(0) = 40 + k, we can solve for C:
-1/200 ln|200(40+k)-(40+k)^2| = 0 + C
C = -1/200 ln|8000-480k|
Plugging in this value of C and simplifying, we get:
-1/200 ln|200P - P^2| = rt - 1/200 ln|8000-480k|
ln|200P - P^2| = -200rt + ln|8000-480k|
|200P - P^2| = e^(-200rt) * |8000-480k|
200P - P^2 = ± e^(-200rt) * (8000-480k)
Since the population is increasing, we choose the positive sign:
200P - P^2 = e^(-200rt) * (8000-480k)
Using the initial condition P(0) = 40 + k, we get:
200(40+k) - (40+k)^2 = (8000-480k)
8000 + 160k - 2400 - 80k - k^2 = 8000 - 480k
k^2 + 560k - 2400 = 0
(k + 60)(k - 40) = 0
Thus, k = -60 or k = 40. Since k represents a growth rate, it should be positive, so we choose k = 40. Therefore, the value of the constant k is option (A) 4.
For the second part of the question, the logistic equation that could model the growth in the graph is option (B) dM/dt = (20-M)*(M-50). This is because the carrying capacity is between 20 and 50, and the population growth rate is zero at both of these values (i.e. the population does not increase or decrease when it is at the carrying capacity).
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a museum gift shop sold 215 sets of dinosaurs. there were 9 dinosaurs in each set how many dinosaurs did they sell?
Use the data set and line plot below. Jerome studied the feather lengths of some adult fox sparrows.
How long are the longest feathers in the data set?
A.
2
2
inches
B.
2
1
4
214
inches
C.
2
1
2
212
inches
D.
2
3
4
234
inches
Answer: 2 1/2
Step-by-step explanation:
the answer is D i took the test here is proof
The values of certain types of collectibles can often fluctuate greatly over time. Suppose that the value of a limited-edition flamingos riding alligators lawn ornament set is found to be able to be modeled by the function V(t) = 0.06t4 – 1.05t3 + 3.47t? – 8.896 +269.95 for Osts 15 where V(t) is in dollars, t is the number of years after the lawn ornament set was released, and t = 0 corresponds to the year 2006. a) What was the value of the lawn ornament set in the year 2009? b) What is the value of the lawn ornament set in the year 2021? c) What was the instantaneous rate of change of the value of the lawn ornament set in the year 2013? d) What is the instantaneous rate of change of the value of the lawn ornament set in the year 2021? e) Use your answers from parts a-d to ESTIMATE the value of the lawn ornament set in 2022.
The value of the lawn ornament set in the year 2009 was $51.375. The value of the lawn ornament set in the year 2021 was $558.181. The instantaneous rate of change of the value of the lawn ornament set in the year 2013 was $230.986. The instantaneous rate of change of the value of the lawn ornament set in the year 2021 was $351.076. The estimated value of the lawn ornament set in 2022 was $909.257.
a)
To find the value of the lawn ornament set in the year 2009, we have to plug in t = 3, as t = 0 corresponds to the year 2006.
V(3) = 0.06(3)4 – 1.05(3)3 + 3.47(3) – 8.896 + 269.95
V(3) = 51.375
So, the value of the lawn ornament set in the year 2009 was $51.375.
b)
To find the value of the lawn ornament set in the year 2021, we have to plug in t = 15, as t = 0 corresponds to the year 2006.
V(15) = 0.06(15)4 – 1.05(15)3 + 3.47(15) – 8.896 + 269.95
V(15) = $558.181
So, the value of the lawn ornament set in the year 2021 is $558.181.
c)
To find the instantaneous rate of change of the value of the lawn ornament set in the year 2013, we have to find V'(7), where V(t) is the given function.
V(t) = 0.06t4 – 1.05t3 + 3.47t – 8.896 +269.95 for Osts 15
V'(t) = 0.24t3 – 3.15t2 + 10.41t + 269.95
V'(7) = 0.24(7)3 – 3.15(7)2 + 10.41(7) + 269.95
V'(7) = $230.986
So, the instantaneous rate of change of the value of the lawn ornament set in the year 2013 was $230.986.
d) To find the instantaneous rate of change of the value of the lawn ornament set in the year 2021, we have to find V'(15), where V(t) is the given function.
V(t) = 0.06t4 – 1.05t3 + 3.47t – 8.896 +269.95 for Osts
15V'(t) = 0.24t3 – 3.15t2 + 10.41t + 269.95
V'(15) = 0.24(15)3 – 3.15(15)2 + 10.41(15) + 269.95
V'(15) = $351.076
So, the instantaneous rate of change of the value of the lawn ornament set in the year 2021 is $351.076.
e)
To ESTIMATE the value of the lawn ornament set in 2022, we can use the formula
V(t) ≈ V(a) + V'(a)(t – a),
where a is the year 2021.
V(a) = V(15) = $558.181
V'(a) = V'(15) = $351.076t = 16 (as we need to estimate the value of the lawn ornament set in 2022)
V(t) ≈ V(a) + V'(a)(t – a)
V(t) ≈ 558.181 + 351.076(16 – 15)
V(t) ≈ $909.257
So, the estimated value of the lawn ornament set in 2022 is $909.257.
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Coronary bypass surgery: A healthcare research agency reported that
41% of people who had coronary bypass surgery in 2008
were over the age of 65. Twelve coronary bypass patients are sampled.
Part 1 of 2
(a) What is the mean number of people over the age of 65 in a sample of 12
coronary bypass patients? Round the answer to two decimal places.
The mean number of people over the age of 65 is ?
Part 2 of 2
(b) What is the standard deviation of the number of people over the age of 65
in a sample of 12 coronary bypass patients? Round the answer to four decimal places.
The standard deviation of the number of people over the age of 65 is ?
The standard deviation of the number of people over the age of 65 in a sample of 12 coronary bypass patients is 1.6487.
Given that a healthcare research agency reported that 41% of people who had coronary bypass surgery in 2008 were over the age of 65 and twelve coronary bypass patients are sampled.
To determine the mean number of people over the age of 65 in a sample of 12 coronary bypass patients, we use the formula below:
Mean = np
Where n = 12 and p = 0.41.
Mean = 12(0.41)
Mean = 4.92
Therefore, the mean number of people over the age of 65 in a sample of 12 coronary bypass patients is 4.92.
To determine the standard deviation of the number of people over the age of 65 in a sample of 12 coronary bypass patients, we use the formula below:
Standard deviation, σ = √(n p q)
Where n = 12, p = 0.41, and q = 1 - p.
Standard deviation, σ = √(12 × 0.41 × 0.59)
Standard deviation, σ = √2.71948
Standard deviation, σ = 1.6487 (rounded to four decimal places).
Therefore, the standard deviation of the number of people over the age of 65 in a sample of 12 coronary bypass patients is 1.6487.
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.
Four different cellular phone plans are shown below.
• Plan 1 charges $0.35 per minute with no monthly fee.
Plan 2 charges a monthly fee of $10.00 plus $0.25 per minute.
• Plan 3 charges a monthly fee of $59.95 with 200 free minutes.
Plan 4 charges a monthly fee of $15.00 plus $0.20 per minute.
Which plan is the least expensive for 200 minutes of cellular phone use?
.
A. Plan 4
B. Plan 3
C. Plan 1
O
D. Plan 2
a cylinder has a volume of 500cm³ and a diameter of 18cm. which of the following is the closest to the height of the cylinder
Step-by-step explanation:
Volume of Cylinder =
[tex]500 {cm}^{3} = \pi {r}^{2} h[/tex]
given d = 18
r = 1/2 x d = 9cm,
[tex]\pi( {9}^{2} )h = 500 \\ 81\pi \: h = 500 \\ h = \frac{500}{81\pi} cm[/tex]
I will leave the answer in terms of Pi as I am not sure how you want to leave your answer as.
Suppose that X₁, X₂,..., X₂ form a random sample from an exponential distribution with an unknown parameter 3. (a) Find the M.L.E. 3 of 3. (b) Let m be the median of the exponential distribution, that is, 1 P(X₁ ≤m) = P(X₁ ≥ m) = 2 Find the M.L.E. m of m. ‹8 ||
(a) MLE of $\lambda$ is obtained by maximizing the log-likelihood. Suppose that X1,X2,…,XnX1,X2,…,Xn are independent and identically distributed exponential random variables with parameter λ, then the probability density function of XiXi is given by $$f(x_i;\lambda) =\lambda e^ {-\lambda x_i}, \quad x_i\geq0. $$
The log-likelihood function is given by$$\begin{aligned}\ln L(\lambda) &= \ln (\lambda^n e^{-\lambda(x_1+x_2+\cdots+x_n)}) \\&=n\ln \lambda-\lambda(x_1+x_2+\cdots+x_n).\end{aligned}$$
The first derivative of the log-likelihood function with respect to λλ is$$\frac {d\ln L(\lambda)} {d\lambda} = \frac{n}{\lambda}-x_1-x_2-\cdots-x_n.$$
The first derivative is zero when $$\frac{n}{\lambda}-\sum_{i=1} ^{n} x_i=0. $$Hence, the MLE of λλ is $$\hat{\lambda} =\frac{n}{\sum_{i=1} ^{n} x_i}. $$
Substituting the value of $\hat{\lambda} $ gives the maximum value of the log-likelihood. So, the MLE of $\lambda$ is given by $$\boxed{\hat{\lambda} =\frac{n}{\sum_{i=1} ^{n} x_i}}. $$
The MLE of $\lambda$ is $\frac {3} {\sum_{i=1} ^{n} x_i}$.
(b) The median of the exponential distribution is given by$$m = \frac {\ln (2)} {\lambda}. $$
Therefore, the log-likelihood function for median is given by$$\begin{aligned}\ln L(m) &= \sum_{i=1}^{n} \ln f(x_i;\lambda)\\&= \sum_{i=1}^{n} \ln \left(\frac{1}{\lambda}e^{-x_i/\lambda}\right)\\&= -n\ln\lambda-\frac{1}{\lambda}\sum_{i=1}^{n}x_i.\end{aligned}$$
The first derivative of the log-likelihood function with respect to mm is$$\frac {d\ln L(m)} {dm} = \frac {1} {\lambda}-\frac {1} {\lambda^2} \sum_{i=1} ^{n}x_i\ln 2. $$
The first derivative is zero when $$\frac {1} {\lambda} =\frac{1}{\lambda^2}\sum_{i=1}^{n}x_i\ln 2.$$Hence, the MLE of mm is $$\boxed{\hat{m} = \frac{\ln 2}{\bar{x}}}.$$where $\bar{x}=\frac{1}{n}\sum_{i=1}^{n}x_i.$Therefore, the MLE of m is $\frac {\ln 2} {\bar{x}}. $
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Answer: The correct answer is A or B
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