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# covariance watch

1. I have the pdf(x) and cdf(x)
and from part (a) worked out PDF(y) and CDF (y) given Y=X^2

how do i work out covariance?
i know cov(x) =E(xy) -E(x)E(y)

the blue bit i can do. its the red bit im stuck on surly you need the joint distribution to work this out???
thanks
2. (Original post by whiterose)
I have the pdf(x) and cdf(x)
and from part (a) worked out PDF(y) and CDF (y) given Y=X^2

how do i work out covariance?
i know cov(x) =E(xy) -E(x)E(y)

the blue bit i can do. its the red bit im stuck on surly you need the joint distribution to work this out???
thanks
I had this same problem the other day but i think i worked it out , Y=X^2
implies E[XY]=E[X^3]

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