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Math Help - increasing decreasing

  1. #1
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    increasing decreasing

    Find the intervals on which y = (x +4)^2 - 7 is increasing or decreasing

    I have never had a problem like this i don't know what to do please help
    thank you!
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  2. #2
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    where did the 9 come from?
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  3. #3
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by aikenfan View Post
    Find the intervals on which y = (x +4)^2 - 7 is increasing or decreasing

    I have never had a problem like this i don't know what to do please help
    thank you!
    Quote Originally Posted by aikenfan View Post
    where did the 9 come from?
    y = (x + 4)^2 - 7 = (x^2 + 8x + 16) - 7 = x^2 + 8x + 9

    -Dan
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    Forum Admin topsquark's Avatar
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    Quote Originally Posted by aikenfan View Post
    Find the intervals on which y = (x +4)^2 - 7 is increasing or decreasing

    I have never had a problem like this i don't know what to do please help
    thank you!
    Actually there's a quicker way. A (vertical) parabola has the form:
    y = a(x - h)^2 + k
    where the vertex is at (h, k) and it opens upward if a > 0 and opens downward if a < 0.

    So the vertex of y = (x + 4)^2 - 7 is at (-4, -7) and a = 1. Thus it opens upward. So it must be decreasing on ( - \infty, -4) and increasing on (-4, \infty).

    -Dan
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