2 cos^3 t + cos^2 t − 2 cos t − 1 = 0
This factors into (cos(t) - 1)(cos(t) + 1)(2cos(t) + 1) = 0 so (i) cos(t) = 1 (ii) cos(t) = -1 (iii) cos(t) = -1/2
(i) cos(t) = 1 implies t = 0 or 2pi
(ii) cos(t) = -1 implies t = pi
(iii) cos(t) = -1/2 implies t = pi/3 or t = 5pi/3
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