# Evaluating this definite integral

• Feb 17th 2009, 04:36 PM
fattydq
Evaluating this definite integral
It's the integral from 1 to 10 of x divided by x^2-4. I'm assuming u would be x^2-4 making du 2x so du/2 would be x. Then would I just be left with 1/2 the integral of 1/u and would have to solve it from there?
• Feb 17th 2009, 04:38 PM
Jester
Quote:

Originally Posted by fattydq
It's the integral from 1 to 10 of x divided by x^2-4. I'm assuming u would be x^2-4 making du 2x so du/2 would be x. Then would I just be left with 1/2 the integral of 1/u and would have to solve it from there?

$\int_1^{10} \frac{x}{x^2-4}\,dx$

then you have a problem at -2 and 2! Your integral is improper!
• Feb 17th 2009, 04:41 PM
fattydq
(Doh)
Quote:

Originally Posted by danny arrigo

$\int_1^{10} \frac{x}{x^2-4}\,dx$

then you have a problem at -2 and 2! Your integral is improper!

What? What does this mean then? I understand it's that way because it'd turn out to be 0 but...it's an online homework assignment and there has to be some sort of response.
• Feb 17th 2009, 06:33 PM
Krizalid
It must be a typo on the problem or those aren't the right bounds.

You're learning how to evaluate definite integrals, but you can't do this one because the function ain't continuous at $x=2.$ Regarding those bounds, we have $1\le x\le10$ and $2$ belongs there.

If the question does not include the $-2$ neither $2,$ then you can evaluate the integral.