求证：(1),sin(a+β)sin(a-β)=sin^2a-sin^2β,(2),cos(a+β)cos(a-β)=cos^2a-sin^2β,(3),sin(a+β) cos(a-β)=sinacosa+sinβcosβ求证：1,角θ为第四象限角的充分必要条件是sinθ0 2,角θ为第二象限角的充分必要条件是cosθ

求证:sin a (1+cos2a)=sin a cos a 求证:sin 2a/1+sin a+cos a=sin a+cos a-1急 求证1+sin a+cos a+2sin acos a/1+sin a+cos a=sin a+cos a 已知sinα=a*sin(α+β) (a>1),求证:tan(α+β)=sinβ/(cosβ-a) 以知cos(a+β )=-1,求证sin(2a+β )+sinβ=0 求证：sin²a+sin²β-sin²a×sin²β+cos²a×cos²β=1x是乘以 在△ABC中,求证；sin^(A/2)+sin^(B/2)+sin^(C/2)=1-2sin(A/2)sin(B/2)sin(C/2） 求证恒等式sin(A+B)sin(A-B)=sin²A-sin²B 求证:sin(a+b)sin(a-b)=sin^2a-sin^2b 求证 1+sin a+cos a+2sin a*cos a/1 +sin a +cos a = sin a+ cos a 有什么思路! 求证：tan a/2＝(1-cos)/sin a=sin a/(cos a+1) 求证 (cos a÷(1-sin a))=((1+sin a)÷cos a) sin(a+b)sin(a-b)=sin2a-sin2b求证 求证：sin(A+B)sin(A-B)=sinAsinA-sinBsinB 求证:(tan a*sin a)/(tan a-sin a)=(tan a+sin a)/(tan a*sin a) 求证：cos^8A-sin^8A=cos2A(1-1/2sin^2A) 求证sin^4a+cos^4a=1-2sin^2acos^2a 求证sin^6A+cos^6A=1-3sin^2Acos^A