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

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

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

In a triangle A B C , prove by vector method that a/(sinA)=b/(sinB)=c/(sinC)

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

Prove that: i) sin(A+B)cos(A-B)-cos(A+B)sin(A-B)=sin2B ii) cos(45^(@)-A)cos(45^(@)-B)-sin(45^(@)-A)sin(45^(@)-B)=sin(A+B)

In DeltaABC , prove that: cos2A+cos2B-cos2C=1-4sinAsinBcosC

In a DeltaA B C prove that cos(A+B)+cos C=0.

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

In a DeltaA B C , prove the following : a\ cos A+b\ cos B+c cos C=2bsinA sin\ Cdot

Prove that in triangle A B C ,cos^2A+cos^2B-cos^2C=1-2sinAsinBcosCdot