(3)令y f(r) glr 则。f(x+△x)8(x)-f(x):g(x+△x) △ g(x)g(x+△x)△x im今y=linU(x+△)-f(x):8(x)-f(x)8(x+△)-8(x △x→0△x△x→0 g(x)g(x+△x)△x (x)8(x)-f(x)g(x) 8(x) 推论1 ∑∫(x)=∑x);特别要注意lu(x)+CI=l(x).4 ( ) (3) , ( ) ( ) ( ) ( ) ( ) ( ) ( ) f x y g x y f x x g x f x g x x x g x g x x x =  +   −  +  =  +   令则 0 0 [ ( ) ( )] ( ) ( ) [ ( ) ( )] lim lim ( ) ( ) x x y f x x f x g x f x g x x g x  →  → x g x g x x x  +  −  −  +  − =  +   2 ( ) ( ) ( ) ( ) ( ) f x g x f x g x g x   − = 推论 1 1 1 [ ( )] ( ) ; n n i i i i f x f x = =    = 特别要注意[ ( ) ] ( ). u x C u x + = 