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I need help with this problem. Please show your work and explain how you rewrote the Pythagorean equation into what they are asking. Thank you so much.

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- Apr 12th 2010, 05:11 PMflorx[Quick Question]Rewriting Pythagorean Identity
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I need help with this problem. Please show your work and explain how you rewrote the Pythagorean equation into what they are asking. Thank you so much. - Apr 12th 2010, 05:16 PMpickslides
- Apr 12th 2010, 05:37 PMflorx
Thank you so much for your quick answer for a). I had forgot you could make 1 = sin t + cos t

Anyways can you check to see if I did b) correctly?

b) cos 2t = (cos t)^2 - (sin t)^2

cos 2t = -sin^2t + cos^2t

cos^2t -sin^2t

(1-sin^2t) + (cos^2t -1)

cos 2t = -sin^2t + cos^2t - Apr 12th 2010, 06:26 PMharish21
If you look at

**pickslides'**post, you can see that he has already done part(b) for you.

$\displaystyle 2\cos^2t-1 = 2\cos^2t-(\sin ^2t+\cos^2t)= 2\cos^2t-\sin ^2t-\cos^2t = \cos^2t-\sin ^2t$

Do you know that $\displaystyle 2\cos^2t-1 = \cos2t$? In fact, this is the part(a) of your question!

And your part (b) is thus proved! - Apr 12th 2010, 06:50 PMflorx
Oh thanks I didn't notice that.