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


LHS = RHS


Hence Proved


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