Solving fourth order differential equation (URGENT) I have two second order differential equation which needs to be solved. x1''(t) = 8 x2(t) x2''(t) = 2 x1(t) I have the initial conditions, x1(0) = 0, x2(0) = 1, and terminal conditions x1(pi/4) = 1, x2(pi/4) = 0. Can anyone help me solve these equations?? What I did was to write the equations in terms of x1 and x2 respectively, but that gives me a fourth order differential x1''''(t) = 16 x1(t) x2''''(t) = 16 x2(t) and I do not know how to solve for these. Can any one help please??