对f(x)=ax+2积分,得 0.5ax^2+2x,把上下限0与1代入得,F（x）=0.5a+2=1 a=-2
对xf(x)=ax^2+2x积分,得 1/3*ax^3+x^2 ,把上下限0与1代入得,E(x)=1/3*a+1＝1/3 也得 a=-2