Compare the results of using Equations (4) and (5).
Equations $(4)$ and (5) give different formulas for the integral of
$\tan ^{-1} x :$
$$
\begin{array}{l}{\text { a. } \int \tan ^{-1} x d x=x \tan ^{-1} x-\ln \sec \left(\tan ^{-1} x\right)+C} \\ {\text { b. } \int \tan ^{-1} x d x=x \tan ^{-1} x-\ln \sqrt{1+x^{2}}+C}\end{array}
$$
Can both integrations be correct? Explain.