证明sin(A+B)sin(A-B)=cos^2B-cos^2A
若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a
cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b) 用三角形证明
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
证明cos(a+b)=cos(a)cos(b)-sin(a)sin(b)详细步骤,书上的证明看不懂.
Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2
sin^2 (A)+sin^2(B)-sin^2(A)sin^2(B)+cos^2(A)cos^2(B)
由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a
cos^2A - cos^2B + sin^2C=2cosA *sinB *sinC证明
如何证明sinA+sinB=2sin((A+B)/2)cos((A-B)/2)
证明cos^2(A+B)—sin^2(A—B)=cos2Acos2B
证明sin(2a+b)/sina-2cos(a+b)=sinb/sina