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Does 1 - sin^2x = cos^2x?

  1. Jan 25, 2012 #1
    1. The problem statement, all variables and given/known data

    My book is showing 1 - (sin^2)x = (cos^2)x, is this true? If so under what subject do I find more information about this. I found cofunction identities where sin(90° - θ) = cosθ but I'm not sure if that's the same thing.

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jan 25, 2012 #2


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    Just rearrange [itex]\sin^2 x + \cos^2 x = 1[/itex], which you recently asked about in another thread.
  4. Jan 25, 2012 #3


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    Yes, draw a right triangle and label one of the angles x. Now label each side a, b and c. Ok so what is sin(x) in terms of a,b,c? So what is sin2(x)? Continue this for cos2(x) and you'll see the result holds.

    Basic trigonometry? After being taught about graphing trig functions I believe you're exposed to more trig identities.
  5. Jan 25, 2012 #4
    thanks, i feel stupid, but at least i know the answer
  6. Jan 25, 2012 #5


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    Nah being stupid would be not knowing the answer in the exam :wink:
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