Solve $\displaystyle {8}{{\cos}^{{2}}{\left({t}\right)}}+{2}{\cos{{\left({t}\right)}}}-{3}={0}$ for all solutions $\displaystyle {0}\le{t}<{2}\pi$

$\displaystyle {t}$ = Preview Question 6  

Give your answers accurate to 2 decimal places, as a list separated by commas