P(X≤b)=P(X<b)=F(b) P(X>a=P(X2a=1-F(a f(x)个 a XCh2-54 P(X  b) = P(X  b) = F(b) P(X  a) = P(X  a) =1− F(a) x f ( x) -10 -5 5 0.02 0.04 0.06 0.08 a