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Math Help - sin and cosine identity!

  1. #1
    Junior Member CONFUSED_ONE's Avatar
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    sin and cosine identity!



    help please! i think the pathagoream[sp*] theorem is used here but i don't know where.
    Last edited by CONFUSED_ONE; April 25th 2006 at 06:46 PM. Reason: reformatting the equation
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    Quote Originally Posted by CONFUSED_ONE


    help please! i think the pathagoream[sp*] theorem is used here but i don't know where.
    This is not really an a problem about solve for x,because any makes it true! This is called an identity problem.
    You need to demonstrate.
    \cos^2x-\sin^2x=2\cos^2x-1
    By Pythagorean Identity you have that,
    \sin^2x=1-\cos^2x
    Thus, (watch those signs )
    \cos^2x-(1-\cos^2x)=2\cos^2x-1
    Thus, we have on Left Hand Side,
    2\cos^2x-1=2\cos^2x-1
    (Note I change the name of this thread for reasons explained above).

    \mathbb{Q}.\mathbb{E}.\mathbb{D}
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  3. #3
    Junior Member CONFUSED_ONE's Avatar
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    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.
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