3. The equation of motion of a general mass-spring system subject to an external force F(t) is mr" + cr' + kr = F(t) where m, c and k are the mass, damping coefficient and spring constant respectively. Let's consider a simple undamped system where m = 1, k = 1, and c= 0 and with forcing function F(t) = 0.5 cos(t) (all in SI units) "+=0.5 cos(1) Find the exact analytic expression for the unique solution satisfying the initial con- ditions x(0) = 20) = 0 and use MATLAB to plot the function (t) for 0 <t<50. In the same figure, plot the lines r(t) = 0.25t and 12(t) = -0.25t as dashed lines. Save the figure as hw3q3.fig and submit it.