Exercise 29 sign of curvature

Vasco,

Regarding 29, part ii, I had $\kappa = \pm\frac{1}{r}$, because I used a factor $(-1)^{\frac{3}{2}} = ((-1)^3)^{\frac{1}{2}} = (-1)^{\frac{1}{2}} = i$ and $(-1)^{\frac{3}{2}} = ((-1)^{\frac{1}{2}})^3 = i^3 = -i$.

Gary