Answer
$\theta=1.29+2k\pi$ and $\theta=5.00+2k\pi$
Six example solutions for $k=0,\pm1$:
$-5.00, -1.29, 1.29, 5.00, 7.57, 11.28$
Work Step by Step
Given $cos\theta=0.28$, use a calculator,
we can find two $\theta$ values in $[0,2\pi],$ as $\theta=1.29, 5.00$
and the general solutions are $\theta=1.29+2k\pi$ and $\theta=5.00+2k\pi$
where $k$ is any integer. Six example solutions for $k=0,\pm1$:
$-5.00, -1.29, 1.29, 5.00, 7.57, 11.28$
