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tbrooks3

Find the minimum value for the function: y = x^2 + 9x + 18

  • one year ago
  • one year ago

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  1. samjordon
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    do u knwo how to complete the square? or do u factor it?

    • one year ago
  2. samjordon
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    lets factor its easy

    • one year ago
  3. tbrooks3
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    its under my quadratic function lesson so idk

    • one year ago
  4. samjordon
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    what 2 numbers when you multiply them =18 and when u add them =9?

    • one year ago
  5. tbrooks3
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    is there a number for that?

    • one year ago
  6. samjordon
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    6*3=18 6+3=9

    • one year ago
  7. tbrooks3
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    ohhh

    • one year ago
  8. tbrooks3
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    so is the answer 9 ?

    • one year ago
  9. samjordon
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    yaaaa factoring i just taught this to my class today. hmmmm nooooo we r factoring. We r trying to figure out 2 numbers that when u mulyiply them give us 18 and when u add them gives us 9

    • one year ago
  10. satellite73
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    finding the zeros is a long and complicated way to find the minimum

    • one year ago
  11. samjordon
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    umm well we can complete the square

    • one year ago
  12. samjordon
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    but i dont think she knows that

    • one year ago
  13. Zarkon
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    use the vertex formula

    • one year ago
  14. satellite73
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    minimum is at the vertex, and first coordinate of the vertex of \[y=ax^2+bx+c\] is always \(-\frac{b}{2a}\)

    • one year ago
  15. tbrooks3
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    when doing the vertx thing... is the second number the minimum?

    • one year ago
  16. satellite73
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    in your case it is \(-\frac{9}{2}\) replace \(x\) by \(-\frac{9}{2}\) to find the minimum

    • one year ago
  17. satellite73
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    minimum means minimum value of \(y\) so it is the second coordinate, not the first

    • one year ago
  18. satellite73
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    so yes, what you said, the second number is the minimum.

    • one year ago
  19. samjordon
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    ohhh i like this method. We never learnt this stuff. Like the textbook always made us complete the square. oh cooll

    • one year ago
  20. tbrooks3
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    can i just plug it into my graphing calculator to get the anwser ?

    • one year ago
  21. satellite73
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    completing the square is for suckers, unless of course you are solving a quadratic equation

    • one year ago
  22. lgbasallote
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    last i heard minimum value was in a calculus class o.O i never knew it was in algebra too

    • one year ago
  23. Lukecrayonz
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    It's in Algebra 2.

    • one year ago
  24. Lukecrayonz
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    You can use a calculator to solve it

    • one year ago
  25. samjordon
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    hahah its in math 11 here in canada

    • one year ago
  26. satellite73
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    \[(-\frac{9}{2})^2+9\times (\frac{-9}{2})+18\] then a calculator if you need one

    • one year ago
  27. satellite73
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    you turn math up to eleven in canada? mine only goes up to ten

    • one year ago
  28. Lukecrayonz
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    Ti-84, input the equation into Y= then click 2nd Trace, and do minimum. It will say "Left bound?", go to the left side of the graph and press enter. Right bound? Obviously, right side. It will say "Guess?", which means put it to where you think the minimum y value is.

    • one year ago
  29. Lukecrayonz
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    So for this, you get x=-4.5 and y=-2.25

    • one year ago
  30. tbrooks3
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    sooo many numbers ... ahhhhh!!! >_< what about TI-83 plus?

    • one year ago
  31. samjordon
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    hahaha grade 11 math lol

    • one year ago
  32. lgbasallote
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    so taking the derivative and equating to zero is another story?

    • one year ago
  33. Lukecrayonz
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    It'll be exactly the same basically I think.

    • one year ago
  34. Lukecrayonz
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    Yes lgb haha

    • one year ago
  35. tbrooks3
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    they give us this freshman yr. imma senior now tryna make it up.. sucks :/

    • one year ago
  36. tbrooks3
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    thanks everyone

    • one year ago
  37. satellite73
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    using the derivative to find the minimum value of a quadratic. like using a glock to kill a wingspanroach

    • one year ago
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