Question 563830
What is theta when cos = -(1/2) ?
Theta can't be the 1st quadrant or
the 4th quadrant because cos is
always (+) there.
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In the 2nd quadrant,  {{{ cos( 120 ) = -(1/2) }}}
This angle is 180 - 60
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In the 3rd quadrant, {{{ cos( 240 ) = -(1/2) }}}
This angle is 180 + 60
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Theta is 120 and 240 degrees