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sugagal

  • 3 years ago

please help solve this F(x)= x2 -5x-36

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  1. satellite73
    • 3 years ago
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    solve what? this is a function. what do you want to do with it?

  2. sugagal
    • 3 years ago
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    zero of the polynomial function

  3. sandra
    • 3 years ago
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    is the first term x^2?

  4. sugagal
    • 3 years ago
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    yes

  5. sandra
    • 3 years ago
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    ok, so you want to know what numbers multiply to get -36 but add to get -5

  6. sugagal
    • 3 years ago
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    ok (x-9) and (X+4)

  7. sandra
    • 3 years ago
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    so options for -36 = (-1, 36), (-2,18), (-3,12), (-6,6), (-9,4), (-12,3)... so on

  8. sandra
    • 3 years ago
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    exactly!

  9. sugagal
    • 3 years ago
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    thats as far as I got

  10. sandra
    • 3 years ago
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    so (x-9) * (x+4) distributes to get the right side of the equation

  11. sandra
    • 3 years ago
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    so what values could x have to make the factored version multiple to zero? it's whatever makes the individual factored terms "0" - since anything multiplied by zero is 0

  12. sandra
    • 3 years ago
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    so the first one is (x-9) = 0 OR (x+4) = 0 - those are the roots, solve for x in each case

  13. sandra
    • 3 years ago
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    in the first case, x=9, since (9-9)=0, and 0*(x+4) = 0. So 9 is one root

  14. sandra
    • 3 years ago
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    what is the other one? it's the number that makes (x+4) = 0

  15. sandra
    • 3 years ago
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    so you can do that =)

  16. sugagal
    • 3 years ago
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    -4

  17. sugagal
    • 3 years ago
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    x=-4

  18. sandra
    • 3 years ago
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    exactly, so you have your two roots =). 9 and -4

  19. sandra
    • 3 years ago
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    So the entire thought process is: 1. F(x)= x^2 -5x-36 - find the roots - ok so that means what values of x makes F(X)=0 2. Oh crap, that's hard to just guess and check. I better factor it. 3. F(x) = (x-9)*(x+4) //factored and equivalent 4. OK, so now it's easy to see. The function will equal zero when either (X-9) =0 , OR (x+4) =0. 5. x=9, or x=-4

  20. sugagal
    • 3 years ago
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    ok, so is that the answer

  21. sandra
    • 3 years ago
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    yes

  22. sandra
    • 3 years ago
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    zero means "where does the function = 0". so you found both places

  23. sugagal
    • 3 years ago
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    oh ok thank you very much for you help

  24. sandra
    • 3 years ago
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    np good luck!

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