Question

Please answer with explanation

Answer 1

$- 1 \: \leqslant \: \cos( \alpha ) \: \leqslant \: 1$

$y \: = \: \cos( \frac{x}{2} )$
$\cos( \alpha ) \: = \: - 1 \: = \: \cos( \frac{x}{2} )$
$\alpha \: = \: {\pi }^{ c}$
$\frac{x}{2} \: = \: \pi$
$x \: = \: 2\pi$