Problem
For x ∈ R, let the function y(x) be the solution of the differential equation: dy/dx + 12y = cos(πx/12), y(0) = 0. Then, which of the following statements is/are true?
A y(x) is an increasing function
B y(x) is a decreasing function
C There exists a real number β such that the line y = β infinitely many points
D y(x) is a periodic function