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anonymous

  • one year ago

Math help!

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  1. ybarrap
    • one year ago
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    Do you know calculus? Or do you need to graph to solve?

  2. anonymous
    • one year ago
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    I know calculus. I have to get the second derivative of this equation correct? And then set it equal to 0 and find the x-values?

  3. ybarrap
    • one year ago
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    If x is an inflection point for y then the second derivative, y″(x), is equal to zero if it exists, but this condition does not provide a sufficient definition of a point of inflection. That's to say that if it y″(x) = 0, then it is not necessarily an inflection point. You are looking for the point where the function goes from concave up to concave down or vice versa. See red in this graph - https://en.wikipedia.org/wiki/Inflection_point#/media/File:Animated_illustration_of_inflection_point.gif

  4. ybarrap
    • one year ago
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    Here is a graph of your function. You can see where your function is concave up and concave down. Where it switches (from down to up or vice versa) is where you will test that in fact the second derivative is zero at that point and confirm that it is an inflection point.

  5. anonymous
    • one year ago
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    Wheres the graph of the function?

  6. anonymous
    • one year ago
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    It concaves up at 3

  7. ybarrap
    • one year ago
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    |dw:1436129525084:dw|

  8. ybarrap
    • one year ago
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    Where it goes from Concave down to Concave up is your inflection point

  9. ybarrap
    • one year ago
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    Now take the second derivative and set equal to zero. The point in that vicinity is the inflection point.

  10. anonymous
    • one year ago
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    I got -3 and 0

  11. ybarrap
    • one year ago
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    The second derivative set equal to zero is d^2/dx^2(x^3+18 x^2-3 x+4) = 6 (x+6) =0 So x = -6, right?

  12. ybarrap
    • one year ago
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    A little cleaner -- $$ \frac{d^2}{dx^2}\left (x^3+18 x^2-3 x+4 \right )=6(x+6)=0 $$ This is your equation, right?

  13. ybarrap
    • one year ago
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    Here is the second derivative - http://www.wolframalpha.com/input/?i=d%5E2%2Fdx%5E2+%28x%5E3+%2B+18x%5E2+%E2%80%93+3x+%2B+4%29

  14. ybarrap
    • one year ago
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    Does this make sense?

  15. anonymous
    • one year ago
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    Okay yeah I messed up when deriving

  16. anonymous
    • one year ago
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    Thank you!

  17. ybarrap
    • one year ago
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    You're welcome

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