$a$ is even number and $b$ is odd number

$a$ is odd number and $b$ is even number

Both $a$ and $b$ are even numbers

Both $a$ and $b$ are odd numbers

$\frac{25}{8} \cos ^{-1}\left(\frac{1}{5}\right)-\frac{\sqrt{6}}{4}$

$\frac{25}{8} \sin ^{-1}\left(\frac{1}{5}\right)-\frac{\sqrt{6}}{4}$

$\frac{\pi}{2}$

$\pi$

$\frac{\pi^2-2}{8}$

$\frac{\pi(\pi-2)}{8}$

$\frac{\pi-2}{8}$

$\frac{\pi+2}{8}$

$\frac{3 \pi}{128}$

$\frac{9 \pi}{32}$

$\frac{9 \pi}{64}$

$\frac{3 \pi}{64}$