# Proving Multiple Angel Formulas

• November 10th 2009, 02:33 PM
ryno16
Proving Multiple Angel Formulas
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cos^2(θ)-sin^2(θ)=2cos^2(θ)-1

and

cos^2(θ)-sin^2(θ)=1-2sin^2(θ)
• November 10th 2009, 02:42 PM
pickslides
$\cos^2(\theta)+\sin^2(\theta)=1$

Therefore

$\sin^2(\theta)=1-\cos^2(\theta)$

So in your problem

$\cos^2(\theta)-\sin^2(\theta)$

becomes

$\cos^2(\theta)-(1-\cos^2(\theta))$

$2\cos^2(\theta)-1$

Use the same idea for the second problem.