Prove by vector method that `cos(A+B)cos AcosB-sinAsinBdot`

Prove by vector method that cos(A+B)=cos A cos B-sin A sin B

Prove by vector method that sin(A-B)=sin A cos B-cos A sin B and sin(A+B)=sin A cos B+cos A sin B

Using vector method prove that cos(A-B)=cosAcosB+sinAsinB

In a triangleABC , prove by vector method that cos2A+cos2B+cos2Cge(-3)/(2) .

Prove by vector methods that sin(alpha+beta)=sin alpha cos beta+cos alpha sin beta

Prove that formula cos(A-B)=cos A*cos B+sin A*sin Bwith the help of the formula sin(A+B)=sin A*cos B+cos A*sin B

For any A,B in R, prove that cos(A-B)=cos A cos B+sin A sin B

Prove that cos(A+B) cos(A-B)-sin(A+B) sin(A-B)=cos 2A.

Prove that a cos A+b cos B+c cos C<=s

Prove that (sin A+sin B)/(cos A+cos B)+(cos A-cos B)/(sin A-sin B)=0