Draw the graph of the following function:

$\cos \frac{x}{2}$

Also write its range and period.

Draw the graph of the following function:

$3\cos 2x$

Also write its range and period.

Draw the graph of the following function:

$2\cos 3x$

Also write its range and period.

Find the value of $k$ if $\cos 210°=-\frac{\sqrt{k}}{2}$.