In each of Problems 7 through 10, find the steady periodic solution x_sp(t) = C cos(ωt - α) of the given equation mx" + cx' + kx = F(t) with periodic forcing function F(t) of frequency ω. Then graph x_sp(t) together with (for comparison) the adjusted forcing function F₁(t) = F(t)/mω.

x" + 4x' + 4x = 10 cos 3t