Fox states in Section 2.4, pg. 38, that
"Anticipating this result, it follows that even if $u(x)$ vanishes at either or both of the values $x=a$ and $x=b$, both $t^2(a)/u(a)$ and $t^2(b)/u(b)$ still vanish since $t(a)=t(b)=0$ by hypothesis."
How does this make sense? The quotient would become $0/0$ in such a case, which is indeterminate, not vanishing.