1-cos2a,cos(a b)

cos^2(a-b-cos^2(a b=1/2(1 cos2a(1 cos2b=1/3
回答 根据cos2a=2cosa^2-1 cos(2(45-b2=cos(90-b=2cos
c的对边分别为abc若sin2a=根号3cos2a,且a为锐角,求
9:这题的重点在于sin2a=2sinacosa 原式=2sinacosa/cos^2a=2tana=6
a,b为锐角,角a,b,c对应的边分别是a,b,c,且cos2a=3/5,sinb=根号10/10