(1)和的分布:Z=X+Y Ch3-120 设(X,Y)的联合d为f(x,y),则 F2(-)=P(Z≤z) =P(X+Y<z =‖f(x,y)oxb x+y<z z-x dx.f(x, y)dy 或 dy f(x, y)dx -<z<+0OCh3-120 (1) 和的分布：Z = X + Y 设( X ,Y )的联合d.f.为 f (x,y), 则 • z • z F (z) P(Z z) Z =  = P(X +Y  z)  +  = x y z f (x, y)dxdy   + − − − = z x dx f (x, y)dy 或   + − − − = z y dy f (x, y)dx −   z  +