Find the domain for 2x^2+7x-5, which is the denominator for a certain fraction.... I did the quadratic formula, and got a weird answer.... can someone please help me?

Question

jim_thompson5910 · Answer

what did you get when you used the quadratic formula?

anonymous · Answer

hold on, let me find my notes.There's stuff all over my room, I am remodeling, and its somewhere...

anonymous · Answer

-7+/-sqrt(89)/4

jim_thompson5910 · Answer

I'm assuming everything is over 4


If so, then you have the correct answer.

jim_thompson5910 · Answer

Those are the zeros. They make the entire polynomial equal to zero.

jim_thompson5910 · Answer

So you have to exclude them from the domain

anonymous · Answer

how would you put that into the form (a,b)?

jim_thompson5910 · Answer

You can either enter them as they are or you can approximate them


So if you use the exact answers, then the domain is 

$$ \left(-\infty, \frac{-7-\sqrt{89}}{4}\right)\cup\left(\frac{-7-\sqrt{89}}{4}, \frac{-7+\sqrt{89}}{4}\right)\cup\left(\frac{-7+\sqrt{89}}{4}, \infty\right)$$


but that is really really messy....


so I'd go with the approximate zeros


The two zeros are approximately -4.108495283 and 0.6084952830


This means we have to exclude these values from the domain


So the domain is $$ \left(-\infty, -4.108495283\right)\cup\left(-4.108495283, 0.6084952830\right)\cup\left(0.6084952830, \infty\right)$$

anonymous · Answer

can you put that in fractional form, please?

jim_thompson5910 · Answer

the first answer is in fractional form

jim_thompson5910 · Answer

but you can't represent the answer in the form a/b where a and b are integers

anonymous · Answer

okay

anonymous · Answer

how about rounding it?

jim_thompson5910 · Answer

to the nearest thousandth, the domain is


$$ \left(-\infty, -4.108\right)\cup\left(-4.108, 0.608\right)\cup\left(0.608, \infty\right)$$

anonymous · Answer

I thought the domain for this one was all real numbers.

jim_thompson5910 · Answer

not if that polynomial is the denominator of some fraction

anonymous · Answer

oh.

jim_thompson5910 · Answer

yeah that was my initial thought too

myininaya · Answer

hopefully the domain of the numerator is all real numbers

jim_thompson5910 · Answer

true...

jim_thompson5910 · Answer

but I'm assuming that the numerator is some polynomial too