http://i10.photobucket.com/albums/a1...oOkIe/MaTH.jpg

help please! i think the pathagoream[sp*] theorem is used here but i don't know where.

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- Apr 25th 2006, 05:45 PMCONFUSED_ONEsin and cosine identity!http://i10.photobucket.com/albums/a1...oOkIe/MaTH.jpg

help please! i think the pathagoream[sp*] theorem is used here but i don't know where. - Apr 25th 2006, 06:09 PMThePerfectHackerQuote:

Originally Posted by**CONFUSED_ONE**

You need to demonstrate.

$\displaystyle \cos^2x-\sin^2x=2\cos^2x-1$

By Pythagorean Identity you have that,

$\displaystyle \sin^2x=1-\cos^2x$

Thus, (watch those signs :eek: )

$\displaystyle \cos^2x-(1-\cos^2x)=2\cos^2x-1$

Thus, we have on Left Hand Side,

$\displaystyle 2\cos^2x-1=2\cos^2x-1$

(Note I change the name of this thread for reasons explained above).

$\displaystyle \mathbb{Q}.\mathbb{E}.\mathbb{D}$ - Apr 25th 2006, 06:32 PMCONFUSED_ONE
thank you thank you thank you ThePerfectHacker!

so i see, it's an idenity problem. haha, you changed the title. thanks.

so you substitue the sin^2X to get 1-cos^2X. i see now. thank you again.

:D