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Homework Help: Trig triangle problem

  1. Apr 14, 2009 #1
    1. The problem statement, all variables and given/known data

    Use the given triangle to prove that for 0 < X <90, 1 + tan^2X = 1 / cos^2X

    (the given triangle is right angled with angle X marked. The hypotenuse is labeled c, adjacent angle is labeled a and the opposite angle is labeled b)

    3. The attempt at a solution

    I have no idea where to begin,
    tanX = b/a
    cosX = a/c
  2. jcsd
  3. Apr 14, 2009 #2


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    Welcome to PF!

    Hi crazy_v! Welcome to PF! :wink:
    But you're there

    just put b/a and a/c into the original equation, and you have … ? :smile:
  4. Apr 14, 2009 #3


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    Since [tex]\cos \theta=\frac{a}{c} \Rightarrow \cos^2 \theta=\frac{a^2}{c^2}[/tex]. Write c^2 in terms of a and b now, hint Pythagoras.
  5. Apr 14, 2009 #4
    thanks guys

    yeah that looks a lot more obvious now, thanks anyways
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