=lim lu(r+h)-u(x)v(x)-u(x)Iv(+h)-v(x) h→>0 (x+)v(r )h u(x+h)-u(r) v(x+h-v(x) .v((x). =lim h→0 v(x+hv(r) u(r)v(x-u(rv(x v(x)I .∫(x)在x处可导v x h v x h u x h u x v x u x v x h v x h ( ) ( ) [ ( ) ( )] ( ) ( )[ ( ) ( )] lim 0 + + − − + − = → ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) lim 0 v x h v x h v x h v x v x u x h u x h u x h + + −  −  + − = → 2 [ ( )] ( ) ( ) ( ) ( ) v x u x v x − u x v x =  f (x)在x处可导