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Thread: Trigonometric Identities.

  1. #1
    Gold is the new black Goldenboko's Avatar
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    Default Trigonometric Identities.

    Still trying to perfect these, I ain't too good at them yet.

    How do I show that (1+cos#)(1-cos#)=sin^2#

    I get to 1-cos^2#=sin^2#

    But then I forget what to do :o

  2. #2
    GO! use leech seed! qwertysaur's Avatar
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    1-cos<sup>2</sup> = sin<sup>2</sup>

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    Gold is the new black Goldenboko's Avatar
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    Seriously? I was hoping it was that easy! xD

    I might be back for more help in a bit xD

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    Draw the Drapes Recognized Member rubah's Avatar
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    don't forget about sec^2=1 + tan^2!

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    Okay, Boko. We get it. You're smart.

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    Gold is the new black Goldenboko's Avatar
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    If I was smart I wouldn't be asking for help Yar-Yars!

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    GO! use leech seed! qwertysaur's Avatar
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    Quote Originally Posted by RubyLapiz View Post
    don't forget about sec^2=1 + tan^2!
    Yeah, there are 5 that you absolutely have to memorize, but 4 of them are derivable from the first

    sin<sup>2</sup> + cos<sup>2</sup> = 1

    subtract sin<sup>2</sup> to get

    cos<sup>2</sup> = 1 - sin<sup>2</sup>

    subtract cos<sup>2</sup> to get

    sin<sup>2</sup> = 1 - cos<sup>2</sup>

    divide by sin<sup>2</sup> to get

    1 + cot<sup>2</sup> = csc<sup>2</sup>

    divide by cos<sup>2</sup> to get

    1 + tan<sup>2</sup> = sec<sup>2</sup>

    Just wait until you get the double angles, half angles and sum and difference equations mixed in there. You will have oh so much fun XD

  8. #8
    Draw the Drapes Recognized Member rubah's Avatar
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    can you post the double angle and half angle formulas? I always forget them.

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    One Hundred Chimneys Recognized Member Tavrobel's Avatar
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    Old school, like an old fool. Flying Mullet's Avatar
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    This is why I like teachers who will let you have a cheat sheet with these identities on tests.
    Figaro Castle

  11. #11
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    Quote Originally Posted by Flying Mullet View Post
    This is why I like teachers who will let you have a cheat sheet with these identities on tests.
    My teacher wants me to memorize them.

  12. #12
    Draw the Drapes Recognized Member rubah's Avatar
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    sadly, calculus teachers are not some of those teachers

    Double Angle Theorem (typed up from tav's link):
    cos(2x )= cos<sup>2</sup>(x) - sin<sup>2</sup>(x)

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