例8设y=sin°x+cosx,求y 解y=(sin2x)3+(os2x)3 =( x+cos x)(sin x-sinf x cos x+cos x) (Sin x+ cos x)"-3sin x cos x 3 =1-sin22x=1 3 1-c0s 4x 2 5+ 3 cos 4x 88 y)=.4"·cos(4x+n 兀、 8 上页例 8 sin cos , . 6 6 (n) 设 y = x + x 求y 解 2 3 2 3 y = (sin x) + (cos x) (sin cos )(sin sin cos cos ) 2 2 4 2 2 4 = x + x x − x x + x x x x x 2 2 2 2 2 = (sin + cos ) − 3sin cos sin 2x 43 1 2 = − 2 1 cos 4 43 1 − x = −  cos 4 x 83 85 = + ). 2 4 cos(4 8 ( ) 3   y =   x + n n n