If correlation coefficient between x and y is 0.5 then r between 4x 2 ...
And 3y - 1 is also 0.5.
To see why this is the case, let's use the formula for the correlation coefficient:
r = (covariance of x and y) / (standard deviation of x * standard deviation of y)
We can rewrite this formula in terms of the variables 4x^2 and 3y-1:
r' = (covariance of 4x^2 and 3y-1) / (standard deviation of 4x^2 * standard deviation of 3y-1)
Now we just need to plug in some values. First, we need to find the covariance of 4x^2 and 3y-1:
cov(4x^2, 3y-1) = E[(4x^2 - E[4x^2]) * (3y-1 - E[3y-1])]
Since we don't know the means of 4x^2 and 3y-1, we'll assume they're both zero (this won't affect the answer, since we're only interested in the correlation coefficient).
cov(4x^2, 3y-1) = E[4x^2 * 3y-1]
= 12 * E[x^2 * y]
Now we need to use the fact that the correlation coefficient between x and y is 0.5:
r = cov(x,y) / (std(x) * std(y))
0.5 = cov(x,y) / (std(x) * std(y))
cov(x,y) = 0.5 * std(x) * std(y)
So we can rewrite the covariance of 4x^2 and 3y-1 as:
cov(4x^2, 3y-1) = 12 * E[x^2 * y]
= 12 * E[(x * sqrt(x))^2 * (y * sqrt(y))^2]
= 12 * E[(x * sqrt(x)) * (y * sqrt(y))]^2
= 12 * (sqrt(E[x^3 * y]) * sqrt(E[x * y^3]))
= 12 * (sqrt(cov(x^3, y^3)) + sqrt(E[x^4] * E[y^4]))
Again, we'll assume that the means of x^3, y^3, x^4, and y^4 are all zero.
cov(4x^2, 3y-1) = 12 * (sqrt(cov(x^3, y^3)) + sqrt(E[x^4] * E[y^4]))
= 12 * (sqrt(E[x^3 * y^3]) + sqrt(E[x^4] * E[y^4]))
Now we need to find the standard deviations of 4x^2 and 3y-1.
std(4x^2) = sqrt(E[(4x^2 - E[4x^2])^2])
= sqrt(16 * E[x^4])
= 4 * sqrt(E[x^4])
Similarly,
std(3y-1) = sqrt(E[(3y-1 - E[3y-1])^2])
= sqrt(9 * E[y^2])
=
If correlation coefficient between x and y is 0.5 then r between 4x 2 ...
2.2
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