How to solve Second order Non linear differential equations?

edit

Hello, Am new to sage math I need to solve a Second order Differential equation , of the form

y''+Q*y'+sin(y) = C. , differentiation w.r.t 't'

I rewrote the equation as a system of first order DE.

y'=v

v'+Q*v+sin(v.t)=C

But i cant figure out how to proceed further, How can i solve The system of equations Numerically? Thanks in advance