I assume the chair moves from "close to the wall", then "far from the wall", then back "close to the wall" ... how much time to go from "close to the wall" back to "close to the wall" again?
that would be the period.
Megan is sitting in a rocking chair. The distance, d(t) between the wall and the rear of the chair varies sinusodally with time t. At t= 1s, the chair is closest to the wall and d(1)=18cm. At t=1.75s the chair is farthest from the wall and d(1.75)=34cm.
a) what is the period of the function?