sin^6a+cos^6a+3sin^2acos^2a=（sin²a＋cos²a）（sin^4a-sin^2acos^2a+cos^4a）+3sin^2acos^2a=sin^4a-sin^2acos^2a+cos^4a+3sin^2acos^2a=sin^4a＋2sin^2acos^2a+cos^4a=（sin²a＋cos²a）²...