7.设fx)可导，y=fanx),则y= y'=2xsec2 x2f(tanx2) 8.设y=cos则y网= 1,cos2x 2 2cos(x2 ( ) cos n 8.设y x y = = ，则 2 7.设f x y f x y ( ) (tan 可导， = = ),则  2 2 2 y x x f x   = 2 sec (tan ) 1 cos 2 2 2 x y = + ( ) 1 2 cos(2 ) 2 n n y x n −  = +