Figure 33-45 depicts a simplistic optical fiber: a plastic core $\left(n_{1}=1.58\right)$ is surrounded by a plastic sheath $\left(n_{2}=1.46\right)$. A light ray is incident on one end of the fiber at angle $\theta$. The ray is to undergo total internal reflection at point $A$, where it encounters the core-sheath boundary. (Thus there is no loss of light through that bound-
ary.) What is the maximum value of $\theta$ that allows total internal reflection at $A$ ?