Error in Problem 1.7

[clarkzhao]

In page 4 the second line, the integrand should be $\exp(\frac{r^2}{2\sigma^2})rdr$ instead of $\exp(\frac{1}{2\sigma^2})rdr$, the $r^2$ term is missing.

[zhengqigao]

Thanks. I have corrected the typo.