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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)

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- Nov 10th 2009, 02:33 PMryno16Proving Multiple Angel Formulas
Show

cos^2(θ)-sin^2(θ)=2cos^2(θ)-1

and

cos^2(θ)-sin^2(θ)=1-2sin^2(θ) - Nov 10th 2009, 02:42 PMpickslides

Therefore

So in your problem

becomes

Use the same idea for the second problem.