Explanation:
The equation that relates the distance from the focus and directrix to any point is
or
Since the directrix is a horizontal line, we will use the second equation.
The vertex lies halfway between the focus and directrix.
Since y=1, is perpendicular to the axis of symmetry, we are going to use the point (0,1) to represent the directrix.
Next, using the y values the number that lies between 7 and 1 is 4 so our vertex is
Our h is 0 and. k is 4.
To find p, the equation of the focus is
So we have
or