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Math Help - Absolute Max / Absolute Min Question

  1. #1
    Junior Member StarlitxSunshine's Avatar
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    Absolute Max / Absolute Min Question

    Find the absolute extrema:

     f(x) = sin x- cos x ; [0, \pi]

    Okay. So first I found the derivative of f(x)

    <br />
f ' (x) = cos x + sin x

    Then, to find the critical points I must set this to zero.

     cos x + sin x = 0

    But I'm a little confused. If they were multiplying, I would do: either cos x = 0 or sin x = 0, right ? But since they're being added, I'm not really sure how to get x = ? so I can continue with the question.
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  2. #2
    Newbie
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    São Tomé
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    help for the exercise

    Hello,
    sen x + cos x = 0
    sen x = - cos x
    (sen x/cos x) = -1
    tg x = -1

    In the interval [0, pi], we have:

    tag x = tag(3.pi/4)

    x = 3.pi/4

    I hope you understand.
    Bye!
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