Prove the following :

cos(A – B) = cos A. cos B + sinA . sin B if A=B=60^o

Solving, L.H.S.

= cos (60^o – 60^o) [Putting the value A=B=60^o]

= cos (0^o)

= 1

Solving, R.H.S.

= cos (60^o) × cos (60^o) + sin (60^o) × sin (60^o) [Putting the value A=B=60^o]

= cos²(60^o) + sin²(60^o)

We know that,

= 1

∴ LHS = RHS

Hence Proved