SOLUTION: What is the minimum value of cos(theta) + 2cos(theta +240)

Set dy/dt = 0 to find critical points:



  



dy/dt is zero at t = -90 degrees  (and every +/- 180 degrees added to that)



zeros are at  t =  degrees 





 n     t (deg)    y

---   -------    ---

 -1     -270     

 0      -90     

 1       90     

 

The minimum value is  (approx. -1.732051) at t=-90 degrees