# Prove the following: Q(6)

Multiply and divide by 2 both cos and sin functions
We get,

Now, we know that

2cosAcosB = cos(A+B) + cos(A-B)             -(i)
-2sinAsinB = cos(A+B) - cos(A-B)               -(ii)
We use these two identities

In our question A =

B =
So,

As we know that

By using this

R.H.S

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