以下用 a^b 表示 a的b次方.= = = = = = = = =因为 (sin x)^4 -(cos x)^4=[ (sin x)^2 +(cos x)^2 ] [ (sin x)^2 -(cos x)^2 ]= -cos 2x=sin (2x -π/2)=sin 2 (x -π/4),又因为 2 sin x cos x =sin 2x,所以 要得到 y...