∫ [0到1] kxdx = (k/2)x^2|(下限0,上限1) = k/2
∫ [1到∞] x^(-3)dx
= -(1/2) x^(-2) |(下限1,上限∞)
= 1/2
k/2 + 1/2 = 1 ---> k=1
概率统计问题,设随机变量X的概率密度f（x）=（详细请见下图）
∫ [0到1] kxdx = (k/2)x^2|(下限0,上限1) = k/2
∫ [1到∞] x^(-3)dx
= -(1/2) x^(-2) |(下限1,上限∞)
= 1/2
k/2 + 1/2 = 1 ---> k=1