4. Consider the forced but undamped system described by the initial value problem = 2. x" x 3coswt, x(0) = 0, x'(0) = (a) Determine the natural frequency of the unforced system. (b) Find the solution x(t) for w 1. (c) Plot the solution x(t) versus t for w = 0.7, 0.8, and 0.9. (Feel free to use technology. MatLab, Mathematica, etc.) Describe how the response x(t) changes as w varies in this interval. What happens as w takes values closer and closer to 1? Briefly explain why the behavior you are observing occurs.