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Math Help - A quick function question

  1. #1
    Senior Member
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    A quick function question

    The question:
    Suppose that f(x) = x + cos(2x), write down f(x + 17\pi)

    My attempt:
    f(x + 17\pi) = x + 17\pi + cos(2(x+17\pi))

    But the answer is, x + 17\pi + cos(2x)

    Why don't we substitute the x inside the cosine function? Thanks!
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by Glitch View Post
    The question:
    Suppose that f(x) = x + cos(2x), write down f(x + 17\pi)

    My attempt:
    f(x + 17\pi) = x + 17\pi + cos(2(x+17\pi))

    But the answer is, x + 17\pi + cos(2x)

    Why don't we substitute the x inside the cosine function? Thanks!
    Use:

    \cos(A+B)=\cos(A)\cos(B)-\sin(A)\sin(B)

    CB
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  3. #3
    Senior Member
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    Thanks dude, you're a champion!
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