(3)(4) uy-uy 证:设f(x) 则有 u(x+h u(x f(x)=lim f(x+h)-f(x v(x+h) v(x) m h→>0 h h->0 h u(x+h)-u(x) v(x+h)-v(x) u(x h m h→>0 v(x+h)v(r) u(xv(x-u(xv(x) 故结论成立 C y2(C为常数) ②0∞推论 h :  u(x)v(x) ( ) ( ) ( ) ( ) ( ) ( ) v x h v x u x h v x u x v x h + + − + (3) ( ) 2 v u v u v v u  −  =  证: 设 f (x) = 则有 h f x h f x f x h ( ) ( ) ( ) lim 0 + −  = → h h lim →0 = , ( ) ( ) v x u x ( ) ( ) v x h u x h + + ( ) ( ) v x u x −       + = → ( ) ( ) lim h 0 v x h v x h u(x + h) − u (x) v(x) h v(x + h) − u(x) − v(x) 故结论成立. ( ) 2 v Cv v C −  =  ( C为常数 ) ( ) ( ) ( ) ( ) ( ) 2 v x u  x v x − u x v  x =