A particle of mass m moves along the x-axis and is acted upon by the restoring force -m(n2 + k2)x and the resistance force -2mkx?, where n, k are positive constants. If the particle is released from rest at x = a, show that, in the subsequent motion
x = (a/n)e-kt (n cos nt + k sin nt).
Find how far the particle travels before it next comes to rest.