§3随机变量的分布函数 P{X≤}=F()=, 3、311 P{<X≤x}=F(=)-F(=) 442 P{2≤X≤3} =F(3)-F(2)+P{X=2} 424 123, 4 1 ) 2 1 } ( 2 1 P{X  = F = , 2 1 4 1 4 3 ) 2 3 ) ( 2 5 } ( 2 5 2 3 P{  X  = F − F = − = , 4 3 2 1 4 3 1 (3) (2) { 2} {2 3} = − + = = − + =   F F P X P X -1 0 1 2 3 x 1 §3 随机变量的分布函数