The task is to express the exact answer in interval notation, restricting your attention to -2π ≤ x ≤ 2π.
The given inequality:
cos(x) ≤ 5/3
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)?