化简(2cos^2a-1)/[2tan(45度-a)*sin^2(45度+a)]急用!
问题描述：
化简(2cos^2a-1)/[2tan(45度-a)*sin^2(45度+a)]
急用!
答
(2(cosx)^4-2(cosx)^2+1/2)/2tan(45-x)[sin(45+x)]^2
=1/2(4(cosx)^4-4(cosx)^2+1)/2tan(45°-x)cos²(45°-x)
=1/2（2cos²x-1）²/2sin（45°-x）cos（45°-x）=1/2cos²2x/sin（90°-2x）=1/2cos²2x/cos2x
=1/2cos2x
答
(2cos^2a-1)/[2tan(45度-a)*sin^2(45度+a)]
=cos2a/[2tan(45度-a)*cos^2(45度-a)]
=cos2a/[2sin(45度-a)*cos(45度-a)]
=cos2a/sin(90度-2a)
=cos2a/cos2a
=1