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Math Help - Trig Identities

  1. #1
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    Trig Identities

    I am not understanding at all how to do the trigonometric identities...
    As far as i know we had 12 of them that we had to memorize, even after memorizing them i am unsure of how to apply them.

    so for my first question the problem says
    (sinx + cosx)(sinx + cosx) -1 / sinxcosx
    multiply and simplify
    the answer is 2 however im unsure how you get that answer.

    also there is

    1 + tan^2(-x) = sec^2(x)
    how do I get both sides to equal the same im suppose to use the more complicated side, but, which identity do I use?
    If there is any easy way to remember the identities and to apply them that would be great..
    thanks in advance
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  2. #2
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    \frac{(\sin{x}+\cos{x})^2 - 1}{\sin{x}\cos{x}} =<br />

    \frac{\sin^2{x} + 2\sin{x}\cos{x} + \cos^2{x} - 1}{\sin{x}\cos{x}}

    now ... what do you know about the sum \sin^2{x} + \cos^2{x} ?



     1 + \tan^2(-x) = \sec^2(x)

    note that \tan^2(x) = [\tan(x)]^2 and that \tan(-x) = -\tan(x)
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  3. #3
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    sin^2x+cos^2x = 1, so
    1 + 2 -1 = 2 oo.....

    ok and then

    1 + tan x^2

    1 + tan x^2 = sec x^2
    oo.... thanks

    ok I understand it when someone tells me what to do, but i cant think of what to use when i have to do it all alone :S

    so i have 2 more problems

    tanx + cosx /1+sinx = secx

    so er...
    sinx/cosx + cosx/1+sinx = secx
    is that correct? where do i go after that? :/


    also

    sinx/sinx - cosx = 1 /1 - cotx

    is there any way of really knowing what you have to use? still confused alot thank you
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  4. #4
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    anyone?
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