HHT = E 2-4xxt+4xtxxt, and E 2 = E, X TX = 1, so 4xtxxt = 4xxt is brought into the original formula.

Then hh t = e-4xx t+4xx t = e

(2) If the average value of X is not easy to hit, use X instead.

If X-(u, 8/n) is known from the title, then it is given by Chebyshev inequality P {| X-ex |