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Math Help - Sin, sec and cosine.

  1. #1
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    Sin, sec and cosine.

    If sec^2(x) – 1 = sin(x) , which one of the following is a possible value for x?

    how do you do this?

    Thanks in advance. I don't get the sin,cosine rules so please help.! =)

    The choices are

    a) - \frac{\pi}{2}

    b)= \frac{\pi}{4}

    c) 0

    d) \frac{\pi}{2}

    e) \frac{\pi}{4}

    thanks in advance!
    Last edited by ThePerfectHacker; October 30th 2008 at 10:37 AM.
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by fabxx View Post
    The choices are

    a) - \frac{\pi}{2}

    b)= \frac{\pi}{4}

    c) 0

    d) \frac{\pi}{2}

    e) \frac{\pi}{4}

    thanks in advance!
    see, by inspection, 0 works. \sec^2 0 - 1 = 1 - 1 = 0 = \sin 0

    note that the left hand side (which is actually \tan^2 x) is an even function, so if (a) and (b) don't work, (d) and (e) would give the same answer and hence not work either. (c) being 0 catches your eye though, and i would test that first, and what do you know, it worked!

    doing this with the algebra would be a bit more complicated and time consuming. so just do the check. you have to check at most 3 values, which you can do pretty quickly if you memorized the trig values for the special angles.
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