Position of the horse after
seconds can be modeled by
.
Where
\
: time in seconds.
: phase shift.
Compare the above equation with
.
Here
and
.
Period 

Period is
.
Here period is
the function reaches a maximum height at
radians.
Phase shift is the difference between the horizontal positions of the function at
and
.

Therefore phase shift is
.
Phase shift
.

Substitute
in
.
Thus, the equation is
.
The equation is
.