SSC CHSL 10 Jan 2017 Shift 3 Paper

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Question : 88 of 100

Marks: +1, -0

What is the value of

cos^2(A\/2)

?

(1 - cosA)/2
(1 + cosA)/2
(1 + sinA)/2
(1 - sinA)/2

Solution:

Using double angle formula, we know that

cos(2θ) = cos^2 θ − sin^2 θ

⇒

cos(2θ) = cos^2 θ

− (1 − cos^2 θ)

⇒

cos(2θ) = 2cos^2 θ -1

Replacing θ by

A/2,

we get :
⇒

cosA = 2cos ^2 ( A /2 ) − 1

⇒

cosA + 1 = 2cos^2 ( A/2)

⇒

(cosA+1)/2=cos^2 (A/2 )

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