gjhfdfg
Finding x intercepts for quadratic functions
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gjhfdfg
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I need help on finding the x intercept on this quadratic function,
|dw:1360627184057:dw|
gjhfdfg
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I do now I think,
gjhfdfg
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Hold on,
gjhfdfg
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Ok, so I solve it like this?
|dw:1360627636615:dw|
Marx
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almost, a= 6 not 6x^2
Marx
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that way you have a number :D
gjhfdfg
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What happens to the x^2?
Marx
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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.
gjhfdfg
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Them 2 solutions got me lost..
jazy
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|dw:1360628346901:dw|
gjhfdfg
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I got that so far,
Marx
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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}}
Marx
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i mean \[x_2= 1-\frac{1}{\sqrt{6}}\]
Marx
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ahem, yeah with -1 ... :)
gjhfdfg
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How did you get the\[\sqrt{24}\] ?
Marx
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\[12^2 - 4\cdot 6 \cdot 5 = 144 - 120 = 24\]
gjhfdfg
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Ah, ok I was thinking 12*12 = 120 instead of 144.
My bad,
gjhfdfg
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But then how did \[2\sqrt{6}\] come in?
gjhfdfg
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The square roots throw me off...
Marx
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\[\sqrt{24}=\sqrt{4\cdot 6} =\sqrt{4} \cdot \sqrt{6} = 2\sqrt{6}\]
gjhfdfg
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Ah ok got it thanks.!
Marx
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you welcome :)
gjhfdfg
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Do we do anything else to it?
Marx
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what do you mean?
gjhfdfg
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Is there anything else I should do to the answer(s)?
None of them match my answer choices
Marx
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hmm what are your choices?
gjhfdfg
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Marx
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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
gjhfdfg
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Ah ok thank you
Marx
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\[\frac{-6\pm\sqrt{6}}{6} = -1 \pm \frac{\sqrt{6}}{6} = -1\pm \frac{1}{\sqrt{6}}\]
gjhfdfg
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Got it.!