1/ x^2-10x - 8

I know I have to solve for zero and factor it but when I do it just comes out 1, -5 but the awnser is -1 ,5 ... I just dont understand why ? Sorry math is the subject I struggle with most .Thank you

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- Jun 6th 2006, 02:35 PMstarbriteAlgebra question
1/ x^2-10x - 8

I know I have to solve for zero and factor it but when I do it just comes out 1, -5 but the awnser is -1 ,5 ... I just dont understand why ? Sorry math is the subject I struggle with most .Thank you - Jun 6th 2006, 02:45 PMThePerfectHackerQuote:

Originally Posted by**starbrite**

$\displaystyle \frac{1}{x^2-10x-8}=??$ - Jun 6th 2006, 02:48 PMstarbrite
oh sorry its f(x)

I have to find the domain of the function . Thanks - Jun 6th 2006, 02:55 PMThePerfectHackerQuote:

Originally Posted by**starbrite**

$\displaystyle \frac{1}{x^2-10x-8}$

It can be any value EXCEPT when the denominator is zero.

Thus,

$\displaystyle x^2-10x-8\not =0$

Since this is not factorable use quadradic formula,

$\displaystyle x=\frac{10\pm \sqrt{100+64}}{2\cdot 1}$

Simplfy,

$\displaystyle x=\frac{10\pm 2\sqrt{41}}{2}$

Thus,

$\displaystyle x=5\pm \sqrt{41}$

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To make things clearly, let me explain,

$\displaystyle \sqrt{100+64}=\sqrt{164}=\sqrt{4\cdot 41}=2\sqrt{41}$

And, in the final step since the numbers shared a common factor namely 2 I divided it out. Important "you cannot cancel out of a sum" meaning you cannot cancel a 2 with the 10 and leave the other 2. You must to cancel both of them whenever you deal with add/subt. - Jun 6th 2006, 03:08 PMstarbrite
oh ok thank u so much