${\tan }^{-1} \left(\frac{4}{5}\right) + {\tan }^{-1} \left(\frac{5}{4}\right) = \_\_\_\_\_\_\_.$

${\cos }^{-1 }\left(-\frac{1}{\sqrt{2}}\right) = \_\_\_\_\_\_.$

$\sin 225° = \_\_\_\_\_\_.$

$\cos \left(\frac{\pi }{5}\right) + \cos \left(\frac{6\pi }{5}\right) = \_\_\_\_\_\_\_.$

If $\sin \theta = -2$ then $\theta$ lies in $\_\_\_\_\_\_$ quadrant

$\frac{6\pi }{5} = \_\_\_\_\_\_\_$ degree.

${\cos }^{-1 }\left(\frac{1}{2}\right) =\_\_\_\_\_\_\_\_.$

If $\tan x = \frac{1}{2}$ and $\tan y = \frac{1}{3}$ then $\tan (x + y) = \_\_\_\_\_\_\_\_.$

$sec \left(\frac{3\pi }{2}+ \theta \right) = \_\_\_\_\_\_.$

$\sin {17}^{\circ }\cos {28}^{\circ }+ \cos {17}^{\circ }\sin {28}^{\circ } = \_\_\_\_\_\_.$