Answer:
cos x = (-1 + √7) / 2
Step-by-step explanation:
cos2x + 2cosx - 2 = 0
2cos²x - 1 + 2cosx - 2 = 0
2cos²x + 2cosx - 3 = 0
cos x = (-2 ± √2²-4*2*(-3)) / 2*2
= (-2 ± √28) / 4
= (-1 ± √7) / 2
-1 ≤ cos x ≤ 1
