When two trigonometric graphs such as sine and cosine intersect, we call that point of intersection a solution of the system of equations. This is the same meaning that solutions of systems of linear equations has.
Solutions of Systems of Sine and Cosine graphs
As you can see from the graph, this system of sine and cosine graphs intersect twice during this interval. They intercept at x = Π/4 as well as at x = 5Π/4