<PRE><B>Question 1143227</B>
&lt;pre&gt;
{{{ y = cos(t) + 2cos(t+240) }}}

{{{ dy/dt = -sin(t) - 2sin(t+240) }}}

Set dy/dt = 0 to find critical points:

{{{ dy/dt = -sin(t) - 2sin(t+240) = 0 }}}  

dy/dt is zero at t = -90 degrees  (and every +/- 180 degrees added to that)

zeros are at  t = {{{ n*180 - 90 }}} degrees 


 n     t (deg)    y
---   -------    ---
 -1     -270    {{{ sqrt(3) }}} 
 0      -90     {{{ -sqrt(3) }}}
 1       90     {{{ sqrt(3) }}}
 
The minimum value is {{{ highlight(-sqrt(3)) }}} (approx. -1.732051) at t=-90 degrees 
 


 *[illustration cos(t)_2cos(t_240)]


</PRE>