谁会这道题啊谁会这道题啊
谁会这道题啊E(x)=∫<-∞,+∞>xf(x)dx=∫<0,1>x*2xdx=2/3.D(x)=∫<-∞,+∞>[x-E(x)]^2*f(x)dx=∫<0,1>(x-2/3)^2*2xdx=∫<0,1>[2x^3-(8/3)x^2+8x/9]dx=1/2-8/9+4/9=1/18.