\(|\overrightarrow A + \overrightarrow B |\, = \,\sqrt {{{(10)}^2} + {{(5)}^2}} \) \( = \,5\sqrt 5 \)
\(\tan \theta = \frac{5}{{10}} = \frac{1}{2}\) \( \Rightarrow \)\(\theta = {\tan ^{ - 1}}\left( {\frac{1}{2}} \right)\)
$\left(\cos 135^{\circ}=-0.7\right.$ આપેલ છે.)