Hi Wilson look at: kill(all)$ assume(%omega > 0)$ eq : 'diff(f(x), x, 2) + sin(x) = 0; atvalue('diff(f(x), x), x = 0, 0)$ atvalue( f(x), x = 0, 1)$ sol : desolve(eq, f(x) ); Maxima uses f(x) and g(x) not x(t). Best Luigi