Question

prove that 2cosA cosB =cos(A+B)+cos(A-B)

Answer 1

hope it helps u...........

Answer 2

taking RHS => cos(A+B) + cos(A-B
=> cosAcosB - sinAsinB + cosAcosB + sinAsinB
=> cosAcosB + cosAcosB
=> 2cosAcosB
I hope it helps.