If A, B, and C are constants then AB is a constant (let's call it 'D') and also BC is a constant (call it 'F'). So the equation is better written as . You can find the value for D using the value of x(t) at t=0, since x(0) = D. Then if there is at least one other point on the graph where for a known value of 't' you know the value for x(t), you can determine the value for F using the relationship .