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yuang's Question
Math
Posted 9 months ago

2. Let (X,Y)(X, Y) be a continuous bivariate random variable having the joint probability density function
f(x,y)=cxy,0xy2
f(x, y)=c x y, \quad 0 \leq x \leq y \leq 2

for some real constant c,f(x,y)=0c, f(x, y)=0 elsewhere.
(e) Compute μX,μY,σX2,σY2,Cov(X,Y)\mu_{X}, \mu_{Y}, \sigma_{X}^{2}, \sigma_{Y}^{2}, \operatorname{Cov}(X, Y), and ρ\rho.

Solution
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Answer from Sia
Posted 9 months ago
Solution by Steps
step 1
To find the mean of XX, μX\mu_X, we integrate xx times the joint probability density function f(x,y)f(x, y) over the entire range of XX and YY
step 2
The integral for μX\mu_X is 020yxcxydxdy\int_0^2 \int_0^y x \cdot cxy \, dx \, dy. Using the result from asksia-ll calculator step 1, we have μX=2c3\mu_X = \frac{2c}{3}
step 3
To find the mean of YY, μY\mu_Y, we integrate yy times the joint probability density function f(x,y)f(x, y) over the entire range of XX and YY
step 4
The integral for μY\mu_Y is 020yycxydxdy\int_0^2 \int_0^y y \cdot cxy \, dx \, dy. Using the result from asksia-ll calculator step 3, we have μY=8c15\mu_Y = \frac{8c}{15}
step 5
To find the variance of XX, σX2\sigma_X^2, we calculate 020y(xμX)2cxydxdy\int_0^2 \int_0^y (x - \mu_X)^2 \cdot cxy \, dx \, dy
step 6
Using the result from asksia-ll calculator step 4, we have σX2=8225c(256c2256c+75)μX2\sigma_X^2 = \frac{8}{225}c(256c^2 - 256c + 75) - \mu_X^2
step 7
To find the variance of YY, σY2\sigma_Y^2, we calculate 020y(yμY)2cxydxdy\int_0^2 \int_0^y (y - \mu_Y)^2 \cdot cxy \, dx \, dy
step 8
Using the result from asksia-ll calculator step 5, we have σY2=128c2(24576c449152c3+38176c213600c+1875)16875μY2\sigma_Y^2 = \frac{128c^2(24576c^4 - 49152c^3 + 38176c^2 - 13600c + 1875)}{16875} - \mu_Y^2
step 9
To find the covariance of XX and YY, Cov(X,Y)\operatorname{Cov}(X, Y), we calculate 020y(xμX)(yμY)cxydxdy\int_0^2 \int_0^y (x - \mu_X)(y - \mu_Y) \cdot cxy \, dx \, dy
step 10
Using the result from asksia-ll calculator step 6, we have Cov(X,Y)=128c2(96c296c+25)(256c2256c+75)16875μXμY\operatorname{Cov}(X, Y) = \frac{128c^2(96c^2 - 96c + 25)(256c^2 - 256c + 75)}{16875} - \mu_X \mu_Y
step 11
To find the correlation coefficient ρ\rho, we use the formula ρ=Cov(X,Y)σXσY\rho = \frac{\operatorname{Cov}(X, Y)}{\sigma_X \sigma_Y}
step 12
Using the results from steps 6, 8, and 10, we calculate ρ\rho
[question number] Answer
Key Concept
To compute the mean, variance, covariance, and correlation coefficient for a continuous bivariate random variable, we use the joint probability density function and integrate over the appropriate ranges.
Explanation
The mean is the expected value of the random variable, the variance measures the spread of the distribution, the covariance indicates the direction of the linear relationship between the variables, and the correlation coefficient measures the strength and direction of the linear relationship between the variables.

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