b
(b) $|A| = 1 + {\tan ^2}\frac{\theta }{2} = {\sec ^2}\frac{\theta }{2}$
$AB = I$ $ \Rightarrow $ $B = I{A^{ - 1}}$
$\frac{{\left[ {\begin{array}{*{20}{c}}1&0\\0&1\end{array}} \right]\,\,\left[ {\begin{array}{*{20}{c}}1&{ - \tan \frac{\theta }{2}}\\{\tan \frac{\theta }{2}}&1\end{array}} \right]}}{{{{\sec }^2}\frac{\theta }{2}}}$= ${\cos ^2}\frac{\theta }{2}\,.\,{A^T}$.