This question is designed to be answered with a calculator.Which are the solutions to the equation cos x = 0.9 over the interval 0 ≤ x ≤ π?

On the interval 0 ≤ x ≤ π, cosine decreases from 1 to −1, so cos x = 0.9 has just one solution there. Using a calculator, x = arccos(0.9) ≈ 0.451 radians. Therefore, the solution is 0.451 only.

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