- #1
terryds
- 392
- 13
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
[/B]
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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