2cos(A+B)/2*sin(A-B)/2*2sin(A+B)/2*cos(A-B)/2=sinBsinC怎么化简成s
2cos(A+B)/2*sin(A-B)/2*2sin(A+B)/2*cos(A-B)/2=sinBsinC怎么化简成s
若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a
sin^2 (A)+sin^2(B)-sin^2(A)sin^2(B)+cos^2(A)cos^2(B)
Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2
化简[sin(2A+B)]/sinA-2cos(A+B)
为什么sin(a+b)-sina=2sin(b/2)cos(a+b/2)
证明三角函数等式sin(A+B)-sinA=2cos(A+B/2)sin(B/2)
证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2
已知向量a=(cosα,sinα) b=(cosβ,sinβ) |a+b|=2|a-b|
在直角三角形ABC中,角ABC的对边分别为abc,B=/3,入sinBsinC=cos^2A-cos^2B+sin^2C
cos(a+B)×cos(a-B)=1/3,求cos^2(a)-sin^2(B)的值
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