化简sin^4a-cos^4a/cos2a

化简sin^4a-cos^4a/cos2a 求证sin^4a-cos^4a=-cos2a 化简[cos(4a-π/2）*sin(π/2-a)*cos2a]/[(1+cos2a)(1+cos4a)*cosa 三角比：[cos(4a-PAI/2)*sin(PAI/2-2a)]/[(1+cos2a)*(1+cos4a)] 求证:sin a (1+cos2a)=sin a cos a cos2A+cos(4π/3-2A）化简, 已知cos2a=（1/4),求cos^4a+sin^4+sin^2acos^2a的值 已知sin(π ／4+a)=12／13,a∈(0,派／4),求cos(a-派／4)/cos2a, 0＜a＜π/4.sin(π/4-a)＝5/13.求cos2a/cos(π/4+a) 已知ab都是锐角,cos（a+b）=4/5,sin（a-b）=5/13,求cos2a 化简sin^2(a)*sin^2(b)+cos^2(a)*cos^2(b)-1/2cos2a*cos2b 化简[2sin2a/(1+cos2a)]*(cos^2a/cos2a)