3.设g(x)= 2-x, x≤0 x<0 x≥0 2-f(x) 训=2+) f(x)≤0 f(x)>0 x<0 x≥0 4.设y=ncas0<x<孕.则 X= -sinx dy dx, dy =-d COSx4 ln cos 0 2 x y x x dy   = 4.设 =   = ，( ),则 2 2 , 0 , 0 ( ) , ( ) , 2 , 0 , 0 x x x x g x f x x x x x  −    = =    +   −  3.设 g f x [ ( )]  =   则 2 ( ) ( ) 0 [ ( )] 2 ( ) ( ) 0 f x f x g f x f x f x  −  =   +  2 2 0 [ ( )] 2 0 x x g f x x x  +  =   +  sin cos x dy dx x − = ， 4 x dy dx  = = −