(1.) I have a "particle in motion" problem that is asking me when a particle is at rest, which I understand to be when velocity = v(t) = 0, so v(t) = - (π/4) sin (πt/4) = 0. The given answer is as follows: - (π/4) sin (πt/4) = 0 sin (πt/4) = 0 πt/4 = πn. t = 0,4,8 seconds. (2.) Can someone please explain to me how 0 becomes πn, and/or what specific mathematical concept(s) I need to review?