Question

cos(a+b)*cos(a-b) is equal to​

Answer 1

Answer:

cos(A+B)+cos(A−B)

As we know;

(Cos(A+B)=cosAcosB-sinAsinB

Cos(A-B)=cosAcosB+sinAsinB)

(cosAcosB−sinAsinB)+(cosAcosB+sinAsinB)

CosAcosB-sinAsinB+cosAcosB+sinAsinB

CosAcosB+cosAcosB-sinAsinB+sinAsinB

CosAcosB+cosAcosB+0

2cosAcosB

cos(A+B)+cos(A−B) =2cosAcosB