2. The characteristic polynomial has roots ? = ±i. We are looking therefore for a
particular solution in the form y = (At + B) cos 2t + (Ct + D) sin 2t. We have then y
= A .... Consequently, at moment of t seconds the spring is by 1. 4 cos 8t feet
down. 6. A fundamental system of solutions of the corresponding homogeneous
equa-. 
