fixed typo

multipleIntegrals/exercisesNontrivialRegions/impossible1.tex

@@ -11,7 +11,7 @@
 \begin{exercise}
   Compute:
   \[
-  \int_0^{\sqrt{\pi/2}}\int_y^{\sqrt{\pi/2} \cos(x^2) \d x \d y}
+  \int_0^{\sqrt{\pi/2}}\int_y^{\sqrt{\pi/2}} \cos(x^2) \d x \d y
   \begin{prompt}
     = \answer{1/2}
   \end{prompt}