A). The trigonometric equation is .

The function cos(x) has a period of 2π, first find all solutions in the interval [0, 2π).

The function cos(x) is positive in first , fourth quadrant.

In first Quadrant, 0 ≤ x ≤ π/2.

In fourth Quadrant, 3π/2 ≤ x ≤ 2π.

, and

So the solutions are

.

, and

.

The solutions are in the interval [0, 2π).