# How do you prove arccos(x/2) + arctan(x) = pi/2?

For example, with $x = 1$, we get
$\arccos \left(\frac{1}{2}\right) + \arctan \left(1\right) = \frac{\pi}{3} + \frac{\pi}{4} = \frac{7 \pi}{12} \ne \frac{\pi}{2}$
It is true only for $x = 0$, $x = \sqrt{3}$, and $x = - \sqrt{3}$.