Let X∼Binomial(n,p)X \sim \text{Binomial}(n, p)X∼Binomial(n,p). Find the covariance between XXX and n−Xn-Xn−X.
−np(1−p)-np(1-p)−np(1−p)
np(1−p)np(1-p)np(1−p)
000
−n2p(1−p)-n^2 p(1-p)−n2p(1−p)