His horizontal distance D(t) (in m) from the center (where being behind the center means a negative distance)
as a function of time t (in seconds) can be modeled by a sinusoidal expression of the form a cos(b. t) + d.
Att = 0, when he pushes off, he is 1 m behind the center, which is as far back as he goes. The swing reaches
the center a seconds later.
Find D(t).
t should be in radians.