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tbrooks3

  • 2 years ago

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

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  1. samjordon
    • 2 years ago
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    do u knwo how to complete the square? or do u factor it?

  2. samjordon
    • 2 years ago
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    lets factor its easy

  3. tbrooks3
    • 2 years ago
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    its under my quadratic function lesson so idk

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

  5. tbrooks3
    • 2 years ago
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    is there a number for that?

  6. samjordon
    • 2 years ago
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    6*3=18 6+3=9

  7. tbrooks3
    • 2 years ago
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    ohhh

  8. tbrooks3
    • 2 years ago
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    so is the answer 9 ?

  9. samjordon
    • 2 years ago
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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

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

  11. samjordon
    • 2 years ago
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    umm well we can complete the square

  12. samjordon
    • 2 years ago
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    but i dont think she knows that

  13. Zarkon
    • 2 years ago
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    use the vertex formula

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

  15. tbrooks3
    • 2 years ago
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    when doing the vertx thing... is the second number the minimum?

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

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

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

  19. samjordon
    • 2 years ago
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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

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

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

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

  23. Lukecrayonz
    • 2 years ago
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    It's in Algebra 2.

  24. Lukecrayonz
    • 2 years ago
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    You can use a calculator to solve it

  25. samjordon
    • 2 years ago
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    hahah its in math 11 here in canada

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

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

  28. Lukecrayonz
    • 2 years ago
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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.

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

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

  31. samjordon
    • 2 years ago
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    hahaha grade 11 math lol

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

  33. Lukecrayonz
    • 2 years ago
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    It'll be exactly the same basically I think.

  34. Lukecrayonz
    • 2 years ago
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    Yes lgb haha

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

  36. tbrooks3
    • 2 years ago
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    thanks everyone

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

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