证明右边=左边 sin²A = cos²(A-B) + cos²B - 2os(A-B)c
sin²A+sin²B=cos²C
cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b) 用三角形证明
若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a
sin²(a+b)+cos²(a+b)=
cos(a-b)cos(b-c)+sin(a-b)sin(b-c)=
证明cos²(A+B)—sin²(A—B)=cos2Acos2B
cos^2A - cos^2B + sin^2C=2cosA *sinB *sinC证明
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.
证明三角函数等式sin(A+B)-sinA=2cos(A+B/2)sin(B/2)
cos^B-cos^C=sin^A,三角形的形状
由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a
sin(A+B/2)=cos(C/2)