Can you reason what will happen when [itex]\tau[/itex] is multiplied by itself? And if you calculate [itex]\tau^3[/itex]?
What will happen in general when we keep multiplying tau by itself?
Remember that disjoint cycles commute. Thus, if [itex]\tau = \tau_1 \tau_2 \dotsc \tau_m[/itex] is a product of disjoint cycles, then [itex]\tau^n = \tau_1^n \tau_2^n \dotsc \tau_m^n[/itex].