The position of the system at the beginning of the half-period is [tex]2\cos(15\cdot0)=2\cos(0)=2[/tex]. The position of the system at the end of the half-period is obtained by plugging in [tex]t=\pi[/tex] (a whole period is [tex]2\pi[/tex]). [tex]2\cos(15\cdot\pi)=2\cdot-1=-2[/tex].
The distance traveled during the half-period is the final period is [tex]|2-(-2)|=|2+2|=|4|=4[/tex]. It traveled 4cm.
