Question

If cos 10º - sin 20º = x, then cos 20° is equal to (a) x2-x xV2 - x? (c) x²√1-x² Ans.(b) (d) x + x +4​

Answer 1

Given, x+

x

1

=2cosθ

⇒(x+

x

1

)

3

=(2cosθ)

3

⇒x

3

+

x

3

1

+3x×

x

1

(x+

x

1

)=8cos

2

θ

⇒x

3

+

x

3

1

+3×2cosθ=8cos

3

θ

⇒x

3

+

x

3

1

=2(4cos

2

θ−3cosθ)

=2cos3θ.

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Answer 2

Step-by-step explanation:

See this attachment..

Hope its help..