Q. 5 C

Prove the following :

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

Answer :

Solving, L.H.S.

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

= cos (0o)

= 1

Solving, R.H.S.

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

= cos2(60o) + sin2(60o)

We know that,

= 1


Hence Proved

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