Question

1. Cos (A-B) = CosA cosB + CosA cosB​

Answer 1

Answer:

To find the value of cos15, we have:

cos(A−B)=cosAcosB+sinAsinB

Putting A=45 and B=30

We get cos(45−30)=cos45cos30+sin45sin30

cos15=21×23+21×21

⇒cos15=223+221=223+1