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August 25th, 2017, 03:50 AM   #1
App
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Quadratic Equations by Completing the Square

Hi,
I'm working on this equation where (b/2)^2 = 8/2=4^2=16. However, I'm stuck where I think I need to square both sides, as you can see a purple star there. I also scratchy on how to factor x^2+4x+8? which the answer becomes in the end is in red. -2 plus or minus sq of 14
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Last edited by skipjack; August 25th, 2017 at 07:55 AM.
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August 25th, 2017, 04:04 AM   #2
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$2x^2+8x+1=0$

$2x^2+8x = -1$

$x^2+4x=-\dfrac{1}{2}$

$x^2+4x+4 = -\dfrac{1}{2} +4$

$(x+2)^2=\dfrac{7}{2}$

$x+2= \pm \sqrt{\dfrac{7}{2}}$

$x = -2 \pm \dfrac{\sqrt{14}}{2} = \dfrac{-4 \pm \sqrt{14}}{2}$
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August 25th, 2017, 09:33 PM   #3
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Thank you!
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August 26th, 2017, 02:14 PM   #4
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Your basic error was that you did not have $\displaystyle x^2+ 8x+ 1$ that you are trying to make a "complete square", you have $\displaystyle 2x^2+ 8x+ 1$ and that "2" multiplying $\displaystyle x^2$ makes all the difference. skeeter took care of that by first dividing the equation by 2.
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