1. The problem statement, all variables and given/known data Hello! The task is to express the exact answer in interval notation, restricting your attention to -2π ≤ x ≤ 2π. 2. Relevant equations The given inequality: cos(x) ≤ 5/3 3. The attempt at a solution I have only one doubt here, and I don't see my mistake. I see that if cos(x) was strictly less than (namely <) 5/3, then the answer is [-2π, 2π]. But the inequality says that cos(x) is less or equal to 5/3, but cos(x) can't be equal to any number larger than 1, because its range is [-1, 1]. Why then this inequality is considered having any solutions at all (because of this "equal to" sign)? Thank you!