例4y=tanx,求y. Af y=(tan xy=(sn x)-(sin x)cosx-sin x(cos)y COSX COSX cOSx+Sin-x secx COS X COS X tan x'=secx结束 例 4 y =tan x  求y 解 x x x x x xx y x 2 cos (sin ) cos sin (cos ) ) cos sin (tan ) (  −  = = = x x x x x 2 2 2 2 2 sec cos1 cos cos sin = = + =  即 (tan x )=sec 2x  解 解 x x x x x xx y x 2 cos (sin ) cos sin (cos ) ) cos sin (tan ) (  −  = = = x x x x x 2 2 2 2 2 sec cos1 cos cos sin = = + = 