Show that if X is a random variable with the mean for which f(x) = 0

Show that if X is a random variable with the mean µ for which f(x) = 0 for x < 0, then for any positive constant a, P(X ≥ a) ≤ µ/a This inequality is called Markov’s inequality, and we have given it here mainly because it leads to a relatively simple alternative proof of Chebyshev’s theorem.