cos(A-B/2)=-1/9,sin(A/2-B)=2/3,且PAI/2小于A小于PAI,0小于B小于PAI/2,求cos(A+B)的值.

证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2B=1 sin(a-b)*cos a-cos(a-b)*sin a=1/5,则cos 2b的值是 由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a sin b解题设a为锐角,证：1、2分之根3乘cos a + 2分之1乘sin a=cos(6分之π-a)2、cos a-sin a=根号2cos(4分之π+a) 若log2/1(sin a)+log2/1(sin b)=2,(27^cos a)^cos b=1/9,cos(2a+2b)=? Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2 已知sin(a+b)sin(a-b)=-1/3,求cos^2a-cos^2b的值 求证1+sin a+cos a+2sin acos a/1+sin a+cos a=sin a+cos a 求证.(2),sin平方a+sin平方b-sin平方a*sin平方b+cos平方a*cos平方b=1 已知cos(a+b)cos(a-b)=1/3,则cos^2a-sin^2b的值是? cos(a+B)×cos(a-B)=1/3,求cos^2(a)-sin^2(B)的值 1/2(cos(2B)-cos(2A))=sin(B)sin(A+B)是怎么导出的 cos^2a-cos^2b=m,那么sin(a+b)sin(a-b)=? 证明sin(A+B)sin(A-B)=cos^2B-cos^2A cos a+cosb=-1/3 sin a+sin b=1/2 求cos(a+b) 已知Cos(a-b/2)=-1/9,Sin(a/2-b)=2/3,0 已知sin^4a/cos^2b+cos^4a/sin^2b=1,求证:sin^4 b/cos^2 a+cos^4b/sin^2a=1 已知(cos^4a)/cos^2b+(sin^4a)/sin^2b=1求证(cos^4b)/cos^2a+(sin^4b)/sin^2a=1 若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a=1.(不用向量怎么证?)