cos(a+b)cos(a-b)=cos^2a-sin^2b 这类型题目怎么做?

Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2 若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a 由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b) 用三角形证明 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平方b-sin平方a 2cos(A+B)/2*sin(A-B)/2*2sin(A+B)/2*cos(A-B)/2=sinBsinC怎么化简成s 已知向量a=(cosα,sinα) b=(cosβ,sinβ) |a+b|=2|a-b| 化简[sin(2A+B)]/sinA-2cos(A+B) sin^2 (A)+sin^2(B)-sin^2(A)sin^2(B)+cos^2(A)cos^2(B) cos(a-b)cos(b-c)+sin(a-b)sin(b-c)= 已知4sin asin b=根号2,4cos a cos b=根号6,则cos 2a+cos 2b的值是?