Q. 113.8( 5 Votes )

Prove the followings identities:

(1 + cos θ)(1 – cos θ) = sin2θ

Answer :

Taking LHS =(1 – cosθ)(1+ cosθ)

Using identity , (a + b) (a – b) = (a2 – b2) , we get


= (1)2 – (cosθ)2


= 1 – cos2 θ


= sin2 θ [ cos2 θ + sin2 θ = 1]


= RHS


Hence Proved


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