Question 865985
Plot {{{ theta }}} on the horizontal axis and
{{{ cos( theta ) }}} on the vertical axis.
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{{{ 4*pi }}} is two cycles of the cos wave.
The cos starts out at +1, then goes to zero,
then to -1, then back to zero ( 1 complete cycle )
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The only places where the cos is positive is
the 1st quadrant and the 4th quadrant.
If {{{ cos( theta ) = 1/2 }}}, then 
{{{ arc cos( 1/2 ) = pi/3 }}} and, also
{{{ arc cos( 1/2 ) =  (5*pi) / 3 }}}
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To get all the angles from {{{ 0 }}} to {{{ 4*pi }}},
You just have to add {{{ 2*pi }}} to these
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{{{ pi/3 + 2*pi = ( 7*pi )/3 }}} and
{{{ ( 5*pi )/3 + 2*pi = ( 11*pi )/3 }}}
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So, the answers are:
{{{ pi/3 }}}, {{{ ( 5*pi ) / 3 }}}, {{{ ( 7*pi ) / 3 }}}, and {{{ ( 11*pi ) / 3 }}}
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Here's the plot:
{{{ graph( 600, 400, -pi/2, 4*pi, -2, 2, cos(x), .5 ) }}}