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Math Help - Domain question.

  1. #1
    Senior Member Stroodle's Avatar
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    Domain question.

    Hi, I'm having a little trouble understanding how the domain of trig problems work. For example:

    If \tan(x)=2 and x\in\left [0,\frac{\pi}{2}\right ] find the exact value of tan(2x)

    Now I know how to solve this and get the answer -\frac{4}{3}, but I don't understand how the answer can have a negative value when tan is positive in the first quadrant. I'm sure it must something to do with the 2x, and that I'm missing something really fundamental here??

    Thanks heaps for your help!
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  2. #2
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    mr fantastic's Avatar
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    Quote Originally Posted by Stroodle View Post
    Hi, I'm having a little trouble understanding how the domain of trig problems work. For example:

    If \tan(x)=2 and x\in\left [0,\frac{\pi}{2}\right ] find the exact value of tan(2x)

    Now I know how to solve this and get the answer -\frac{4}{3}, but I don't understand how the answer can have a negative value when tan is positive in the first quadrant. I'm sure it must something to do with the 2x, and that I'm missing something really fundamental here??

    Thanks heaps for your help!
    2x is in the second quadrant ....
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