概车纶与款理统外 0, x<0, x2 0≤x<3, 即F(x)= 12' -3+2r2 ， 3≤x<4, 1, x≥4. PI<K孕=F-0=装          − + −      = 1, 4. , 3 4, 4 3 2 , 0 3, 12 0, 0, ( ) 2 2 x x x x x x x 即 F x } 2 7 (3) P{1  X  ) (1) 2 7 = F( − F . 48 41 =