Question 1176516
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It's a quadratic equation with cos(t) as the variable.  Solve like a quadratic polynomial equation:
(1) get everything on one side, set equal to 0 on the other side
(2) factor the quadratic
(3) the solutions are whatever makes either factor equal to 0<br>
{{{2*cos(t)^2-3*cos(t)=-1}}}
{{{2*cos(t)^2-3*cos(t)+1=0}}}
{{{(2cos(t)-1)(cos(t)-1)=0}}}
{{{2cos(t)=1}}} or {{{cos(t)=1}}}<br>
You can finish from there.<br>