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What is the sum of all roots of 2cos²x + cos x - 1 = 0 in [0, 2π)?
A3π
B4π
C2π
D5π
Answer & Solution
Correct answer: A. 3π
It factors as (2cos x - 1)(cos x + 1) = 0, giving π/3, 5π/3 and π, which sum to 3π.
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