$E(X)=2$ and $E(X(X−1))=5$. Find $V(X)$?
I know that $E(X(X−1))= E(X^2-X) = 5$
and that $V(X) = E(X^2)−[E(X)]^2$
But I do not know how to solve this problem.
2026-03-28 07:36:40.1774683400
$E(X)=2$ and $E(X(X−1))=5$. Find $V(X)$?
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Expectation is linear, hence:
$5=E[X^2-X]=E[X^2]-E[X]=E[X^2]-2$
So $E[X^2]=7$. Can you finish from here?