I am solving and plotting mechanical spring vibration problems, and I keep getting an empty plot for this equation: y''+4y=2cos2t, y(0)=0,y'(0)=0. Here is how I entered it. Any help would be greatly appreciated. Thanks. e2:=(diff(y(t), t, t))+4*y(t) = 4*cos*t; s2:=dsolve([e2, y(0) = 0, (D(y))(0) = 0]); r2; rhs(s2); plot(r2, t = 0 .. 10); Error, empty plot

I am having the hardest time plotting the qualitative behavior of the solutions of these differntial equations. I keep getting Error, (in plots/animate) no non-zero vectors found. If someone could walk me through plotting these equations, it would be greatly appreciated. Equation1: dx/dt=x^2, x(0)=1, 0≤t<>