Differential equations

Solve the system of differential equations

 \ddot y_1 = y_1 + 2 y_2 -2\dot y_1 + 5\cos(2t)  \\ \ddot y_2 = 2y_1 + y_2 -2\dot y_2 - 2\cos(2t)

where y_i=y_i(t).