dIn u 1 aP aQ k ay dr=f(x) f∫(x)tc u(x)=e b当只与有关时.0=0, du ax ay dy dInu 1ao aP 小 y P ar ay 3y(y) u()=ea(y)dyb.当只与y有关时; ( ) ln 1 x Q y P dx Q d   −    =  = f (x) ( ) . ( )   = f x dx  x e = 0,   x  , dy d y   =   ( ) ln 1 y P x Q dy P d   −    =  = g( y) ( ) . ( )   = g y dy  y e