cos(B/2)sin(B/2)=1/4,求角B

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) 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 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?) Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2 cos^4a/(cos^2b)+sin^4a/(sin^2a)=1 求证cos^4b/(cos^2a)+sin^4a/(sin^2b)=1 已知sin[a-b]cos a-cos[b-a]sin a=3/5,b是第三象限角,求sin[b+5π/4]的值第一题1/2cos x-√3/2sin x第二题√3sin x+cos x第三题√2[sin x-cos x]第四题√2cos x-√6sin x cos(B/2)sin(B/2)=1/4,求角B 1/2(cos(2B)-cos(2A))=sin(B)sin(A+B)是怎么导出的 已知sin(a+b)sin(a-b)=-1/3,求cos^2a-cos^2b的值 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 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 求证cos(a+b)cos(a－b)=cos^2b－sin^2a