(1)(u±v)y=±y' 证:设f(x)=(x)士v(x),△x=h,则 f"(x)=lim f(x+h)-f(x) h>0 h lim [u(x+h)士v(x+h]-[u(x)±v(x)] h->0 h lim (x+h)-u(x) ±lim v(x+h)-v(x) h-0 h h->0 h =u'(x)士v(x) 故结论成立 此法则可推广到任意有限项的情形例如, (u+v-w)'=u+y'-w BEIJING UNIVERSITY OF POSTS AND TELECOMMUNICATIONS PRESS 目录 上负 返回 结束目录 上页 下页 返回 结束 此法则可推广到任意有限项的情形. 证: 设 则 (1) (u v) u v 故结论成立. 例如, f (x) u(x) v(x) ,x h, 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) (u v w) u v w