例4.求函数y=√x的导数 解:(1)亼y=√x+Ax-√x (2) x+△v △x(√x+△x+√x)√x+△x+ (3)y=lim=lm - >0√x+△x+结束 解  例 4 求函数 y = x 的导数 解 ( 1 ) y = x + x − x  (2) x x x x x x x x x x x x xy +  + =  +  +  =  +  − =  1 ( )  (3) x x x x x y y x x 2 1 1 lim lim 0 0 = +  + =  = →  →  (2) x x x x x x x x x x x x xy +  + =  +  +  =  +  − =  1 ( ) (2)  x x x x x x x x x x x x xy +  + =  +  +  =  +  − =  1 ( )  (3) x x x x x y y x x 2 1 1 lim lim 0 0 = +  + =   =  →  → (3)  x x x x x y y x x 2 1 1 lim lim 0 0 = +  + =   =  →  → 