Question 312678
I think you mean {{{theta}}}? It's the Greek letter theta.
{{{cos(theta)=-1/2}}}
{{{theta=arccos(-1/2)=120}}} or {{{theta=240}}}
Those values are in degrees.
Use the conversion factor,
{{{2*pi}}} radians={{{360}}} degrees to convert to radians.
{{{120*(2*pi/360)=2*pi/3}}}
{{{240*(2*pi/360)=4*pi/3}}}
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I think you mentioned that
{{{theta <= 3*pi/2}}} so both the answers would meet that criteria.