(0≤x≤1)
F(x)=∫(-∞,+∞)f(x)dx
=∫[0,x]f(t)dt
=∫[0,x]tdt
=t^2/2[0,x]
=x^2/2
1≤x≤2时
F(x)=∫(-∞,+∞)f(x)dx
=∫[0,1]tdt +∫[1,x](2-t)dt
=1/2+(2t-t^2/2)[1,x]
=1/2+2x-x^2/2-2+1/2
=2x-x^2/2-1
x≥0时
F(x)=1
P{x>=1/2}=1-F(1/2)=1-(1/2)^2/2=7/8
P{1/2
设随机变量X的概率密度为f(x)={x,0