# Homework Help: Integral of xln(x) with 0 as a limit of integration

1. Oct 30, 2011

### fixed_point

1. The problem statement, all variables and given/known data
Not exactly a homework problem, but I noticed that wolfram alpha gives
$\displaystyle{\int_{0}^{1}}x\ln{x}\,dx=-\frac{1}{4}$
I was wondering why this is so.

2. Relevant equations & solution attempt
For $\epsilon>0$
$\displaystyle{\int_{\epsilon}^{1}}x\ln{x}\,dx=-\frac{1}{4}-\left(\frac{1}{4}\epsilon^2(2\ln{\epsilon}-1)\right)$
Taking $\epsilon \to 0$ gives the answer provided by wolfram alpha.

My question is what justifies this last step of taking $\epsilon \to 0$? Continuity?

2. Oct 30, 2011

### Dick

It's the definition of an indefinite integral with a singularity at one end of the interval of integration.

3. Oct 30, 2011