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gjhfdfg

  • 2 years ago

Finding x intercepts for quadratic functions

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  1. gjhfdfg
    • 2 years ago
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    I need help on finding the x intercept on this quadratic function, |dw:1360627184057:dw|

  2. Marx
    • 2 years ago
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    do you know the formula? http://en.wikipedia.org/wiki/Quadratic_equation#Quadratic_formula

  3. gjhfdfg
    • 2 years ago
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    I do now I think,

  4. gjhfdfg
    • 2 years ago
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    Hold on,

  5. gjhfdfg
    • 2 years ago
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    Ok, so I solve it like this? |dw:1360627636615:dw|

  6. Marx
    • 2 years ago
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    almost, a= 6 not 6x^2

  7. Marx
    • 2 years ago
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    that way you have a number :D

  8. gjhfdfg
    • 2 years ago
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    What happens to the x^2?

  9. Marx
    • 2 years ago
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    well: a,b and c are the coefficients so there's no need for x's. check the formula again. so you should have two solutions.

  10. gjhfdfg
    • 2 years ago
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    Them 2 solutions got me lost..

  11. jazy
    • 2 years ago
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    |dw:1360628346901:dw|

  12. gjhfdfg
    • 2 years ago
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    I got that so far,

  13. Marx
    • 2 years ago
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    it goes like this: \[x_{1,2} =\frac{-12\pm \sqrt{12^2-4\cdot 6 \cdot 5}}{6\cdot 2} = -1\pm \frac{\sqrt{24}}{12}=-1\pm\frac{2\sqrt{6}}{12}=-1\pm\frac{1}{\sqrt6}\] so we have : \[x_1 = 1+\frac{1}{\sqrt{6}}\] and x_2 = 1-\frac{1}{\sqrt{6}}

  14. Marx
    • 2 years ago
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    i mean \[x_2= 1-\frac{1}{\sqrt{6}}\]

  15. Marx
    • 2 years ago
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    ahem, yeah with -1 ... :)

  16. gjhfdfg
    • 2 years ago
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    How did you get the\[\sqrt{24}\] ?

  17. Marx
    • 2 years ago
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    \[12^2 - 4\cdot 6 \cdot 5 = 144 - 120 = 24\]

  18. gjhfdfg
    • 2 years ago
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    Ah, ok I was thinking 12*12 = 120 instead of 144. My bad,

  19. gjhfdfg
    • 2 years ago
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    But then how did \[2\sqrt{6}\] come in?

  20. gjhfdfg
    • 2 years ago
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    The square roots throw me off...

  21. Marx
    • 2 years ago
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    \[\sqrt{24}=\sqrt{4\cdot 6} =\sqrt{4} \cdot \sqrt{6} = 2\sqrt{6}\]

  22. gjhfdfg
    • 2 years ago
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    Ah ok got it thanks.!

  23. Marx
    • 2 years ago
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    you welcome :)

  24. gjhfdfg
    • 2 years ago
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    Do we do anything else to it?

  25. Marx
    • 2 years ago
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    what do you mean?

  26. gjhfdfg
    • 2 years ago
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    Is there anything else I should do to the answer(s)? None of them match my answer choices

  27. Marx
    • 2 years ago
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    hmm what are your choices?

  28. gjhfdfg
    • 2 years ago
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  29. Marx
    • 2 years ago
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    so it's the second one: \[\frac{-6\pm \sqrt{6}}{6}\] it's basically what I told you but in a different form

  30. gjhfdfg
    • 2 years ago
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    Ah ok thank you

  31. Marx
    • 2 years ago
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    \[\frac{-6\pm\sqrt{6}}{6} = -1 \pm \frac{\sqrt{6}}{6} = -1\pm \frac{1}{\sqrt{6}}\]

  32. gjhfdfg
    • 2 years ago
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    Got it.!

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