If , then the solutions for are all primitive roots of unity.
Find .
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We are given that x + x 1 = 3 . Multiplying by x gives x 2 − 3 x + 1 = 0 .
Applying the quadratic formula, we see that x = 2 3 ± i ⟹ x = { 2 3 + 2 i , 2 3 − 2 i } ∴ x = e π i / 6 , e 1 1 π i / 6
Since an n t h root of unity is defined as e 2 k π i / n for k = 1 , 2 , 3 , . . . , n , these are primitive ( 2 × 6 ) t h = 1 2 t h roots of unity.