fixed typo

Author: bartsnapp

improperIntegrals/digInImproperIntegrals.tex

@@ -380,7 +380,7 @@ \section{Unbounded intervals}
 
 \begin{align*}
 \int_{-\infty}^{\infty} \frac{1}{1+x^2} \d x&= \int_{-\infty}^{0} \frac{1}{1+x^2} \d x + \int_{0}^{\infty} \frac{1}{1+x^2} \d x \\
-& =\lim_{a \to -\infty} \int_{a}^{0} \frac{1}{1+x^2} \d x + \lim_{b \to \infty} \int_{0}^{\infty} \frac{1}{1+x^2} \d x 
+& =\lim_{a \to -\infty} \int_{a}^{0} \frac{1}{1+x^2} \d x + \lim_{b \to \infty} \int_{0}^{b} \frac{1}{1+x^2} \d x 
 \end{align*}
 
 Now we must look at each integral separately.