1lim(x→-∞)F（x）=a-πb/2=0;lim(x→+∞)F（x）=a+πb/2=1;联立得a=1/2;b=1/π.2F（x）=1/2+(1/π)arctanx;F（1）-F（-1）=(1/π)arctan1-(1/π)arctan(-1)=(2/π)arctan1=1/2;3:概率密度为分布函数的微分：f(x)=d...