fjyt001
幼苗
共回答了19个问题采纳率:89.5% 举报
∫(-∞,+∞) f(x) dx=∫[0,1] (a+bx^2)dx= ax+1/3*bx^3 | [0,1]=a+b/3=1 ,-----------(1)
E(x)=∫[0,1](ax+bx^3)dx=1/2*ax^2+1/4*bx^4 | [0,1]=a/2+b/4=0.6,----------(2)
解得 a=0.6,b=1.2,
D(x)=E(x^2)-(E(x))^2=∫[0,1](ax^2+bx^4)dx-0.6^2=1/3*ax^3+1/5*bx^5 | [0,1]-0.6^2
=0.2+1.2/5-0.6^2=0.08 .
1年前
6