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anonymous

  • 4 years ago

how do you complete the square on this 7x^2 + 10x = -2

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  1. amistre64
    • 4 years ago
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    by keeping your wits about you

  2. amistre64
    • 4 years ago
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    factor out the 7 on the left and work out the square part

  3. anonymous
    • 4 years ago
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    divide by 7 first?

  4. amistre64
    • 4 years ago
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    \[7x^2+10x=-2\] \[7(x^2+\frac{10}{7}x)=-2\] \[7(x^2+\frac{10}{7}x+(\frac{10}{14})^2)=-2+7(\frac{10}{14})^2\]

  5. amistre64
    • 4 years ago
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    then I spose we can get rid of that 7 by dividing both sides :)

  6. amistre64
    • 4 years ago
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    \[x^2+\frac{10}{7}x+(\frac{10}{14})^2=-\frac{2}{7}+(\frac{10}{14})^2\] compact the left \[(x+\frac{10}{14})^2=-\frac{2}{7}+(\frac{10}{14})^2\] and work the rest thru

  7. amistre64
    • 4 years ago
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    yes, divide off the 7 first :)

  8. anonymous
    • 4 years ago
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    i can get to the point where i get (x = (10/14))^2 = 44/196 but dont know what to do after this

  9. amistre64
    • 4 years ago
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    you sqrt the sides to unto the ^2 and add off the 10/14

  10. anonymous
    • 4 years ago
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    is the answer (-5+ Sqrt11)-14

  11. amistre64
    • 4 years ago
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    \[\sqrt{(x+\frac{10}{14})^2=-\frac{2}{7}+(\frac{10}{14})^2}\] \[x+\frac{10}{14}=\pm\sqrt{-\frac{2}{7}+(\frac{10}{14})^2}\] \[x=-\frac{10}{14}\pm\sqrt{-\frac{2}{7}+(\frac{10}{14})^2}\]

  12. anonymous
    • 4 years ago
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    i mean (-5 + sqrt11)/14

  13. amistre64
    • 4 years ago
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    the sqrt has 2 parts to it a + and a - that has to be accounted for

  14. amistre64
    • 4 years ago
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    x^2 = 4 x = sqrt(4) x = 2, or -2

  15. amistre64
    • 4 years ago
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    heres a simple dbl chk http://www.wolframalpha.com/input/?i=7x%5E2+%2B+10x+%3D+-2

  16. amistre64
    • 4 years ago
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    looks to be a /7 not /14

  17. anonymous
    • 4 years ago
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    ok thanks a mill

  18. amistre64
    • 4 years ago
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    yep

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