1. The problem statement, all variables and given/known data d) When is the particle moving in the positive direction? [itex]f(t) = cos(πt/4), t ≤ 10[/itex] 2. Relevant equations [itex]f '(t) = -(π/4)sin(π(t)/4)[/itex] 3. The attempt at a solution [itex]0 < -(π/4)sin(π(t)/4)[/itex] [itex](π(t)/4)>πn[/itex] [itex]t>4n 0<=n<=2[/itex] [itex]t>4 t>8[/itex] The answer says 8>t>4 im probably skipping a simple step. wut do?