Eugene E. answered • 08/31/17

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University Physics, Electrodynamics, and Quantum Mechanics Tutor

^{2 }- x - 1 = 0, or (2x + 1)(x - 1) = 0. The roots are x = -1/2, 1. So cos t = -1/2, 1. The solutions you found are the solutions to cos t = -1/2 in [0, 2π). The third solution is t = 0, which comes from solving cos t = 1 in [0, 2π).