例3.求函数y=-的导数 解:(1)Ay 1_-Ax x+△xxx(x+△x) (2) △xx(x+△x) B)y=lim m Ax>0Axx>0x(x+△x)x2 例4.求函数y=√x的导数 解:(1)Ay=√x+Ax-√x; (2) △y x+△x △x △x △x(√x+Ax+√x)√x+Ax+√x (3)y=lim a=lim x+△x+x-2x 首页上页返回下页 结束 铃首页 上页 返回 下页 结束 铃 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 x y + + =  + +  =  + − =   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 x y + + =  + +  =  + − =   1 ( ) (2)  x x x x x x x x x x x x x y + + =  + +  =  + − =   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 = + + =    =  →  →  解 例 3 求函数 x y 1 = 的导数 解 (1) ( ) 1 1 x x x x x x x y + − − = +  =  (2) ( ) 1 x x x x y + =−    (3) 2 0 0 1 ( ) 1 lim lim x x x x x y y x x =− + =−    =  →  →  解 (1) ( ) 1 1 x x x x x x x y + − − = +  =  (3) 2 0 0 1 ( ) 1 lim lim x x x x x y y x x =− + =−    =  →  → (3)  2 0 0 1 ( ) 1 lim lim x x x x x y y x x =− + =−    =  →  →  下页