[" 9.Prove,by vector method,that: "],[cos(A+B)=cos A cos B-sin A sin B" ."]

Prove by vector methods. cos(A- B) = cos A cos B + sin A sin B.

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

Prove 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

Prove that : 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 sin (A+B)= sin A cos B + cos A sin B.

Prove that : sin(A + B) = sin A cos B + cos A sin B .

If A,B,(A - B)are positive acute angles, then prove that geometrically : cos (A - B) = cos A cos B + sin A sin B

Prove that a cos A+b cos B+c cos C=4R sin A sin B sin C