2{cos ^2}θ - 2{sin ^2}θ = 1 , तो θ = .......... ^o

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3.Trigonometrical Ratios, Functions and Identities

easy

$2{\cos ^2}\theta - 2{\sin ^2}\theta = 1$, तो $\theta =$ ..........$^o$

A

$15$

B

$30$

C

$45$

D

$60$

Solution

(b) $2{\cos ^2}\theta – 2{\sin ^2}\theta = 1$

==> $2\cos 2\theta = 1$

==> $\cos 2\theta = \frac{1}{2} = \cos {60^o}$

==> $2\theta = {60^o}$

$\Rightarrow \theta = {30^o}$.

Standard 11

Mathematics

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