dIn u 1 aP aQ o ay ax f(x)dc u(x)= b当只与有关时:Ooo_l ax’ayd dInu 1 ao aP g(y) 小 P ar ay sejs(v)( ) ln 1 x Q y P dx Q d   −    =  = f (x) ( ) . ( )   = f x dx  x e b.当只与y有关时; = 0,   x  , dy d y   =   ( ) ln 1 y P x Q dy P d   −    =  = g( y) ( ) . ( )   = g y dy  y e