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Question:

Let f:[0, 4π] → [0, π] be defined by f(x) = cos⁻¹(cos x). The number of points x ∈ [0, 4π] satisfying the equation f(x) = 10 - x/10 is ................

Solution:

f:[0,4π]→[0,π], f(x) = cos⁻¹(cos x) ⇒ points A, B, C satisfy f(x) = 10 - x/10. Hence, 3 points