(a)
$I_{8} + I_{6} = \int_{0}^{\frac{\pi}{4}}{\tan^{8}{\theta\ d\theta}} + \int_{0}^{\frac{\pi}{4}}{\tan^{6}{\theta\ d\theta}}$
$= \int_{0}^{\frac{\pi}{4}}{\sec^{2}\theta}\tan^{6}\theta d\theta$
$= \left\lbrack \frac{\tan^{7}\theta}{7} \right\rbrack_{0}^{\frac{\pi}{4}} = \frac{1}{7}$