(1)(ty)y=l± 证:设f(x)=l(x)±w(x),则 f(x)=lim f(x+h)-f(x) h->0 h [(x+h)±v(x+h)]-[(x)±v(x)] m h->0 h -lim u(x+h)-u(x) ±lim v(x+h)-v(x) h->0 h h->0 h l(x)±y(x) 故结论成立 此法则可推广到任意有限项的情形例如 例如,(u+y-w)=+v-w ②0∞此法则可推广到任意有限项的情形. 证: 设 , 则 (1) (u  v) = u  v  f (x) = u(x)  v(x) h f x h f x f x h ( ) ( ) ( ) lim 0 + −  = → h u x h v x h u x v x h [ ( ) ( )] [ ( ) ( )] lim 0 +  + −  = → h u x h u x h ( ) ( ) lim 0 + − = → h v x h v x h ( ) ( ) lim 0 + −  → = u (x)  v (x) 故结论成立. 例如