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## Homework Statement

What is the value of ## \frac{1}{cos^2 10^{\circ}}+\frac{1}{cos^2 20^{\circ}}+\frac{1}{cos^2 40^{\circ}}-\frac{1}{cos^2 45^{\circ}} ## ?

A. 1

B. 5

C. 10

D. 15

E. 20

## Homework Equations

cos^2 x + sin^2 x = 1

sin 2x = 2 sin x cos x

cos 2x = cos^2 x-sin^2 x

## The Attempt at a Solution

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I'm only able to determine cos 45 degrees which is √2 / 2

I have no idea about cos 10, cos 20, and cos 40 degrees

Please help me

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