What is the equation of the quadratic graph with a focus of 4,0 and a directrix of y=10

To solve this problem youu must apply the procedure shown below:

 1. Let's call (x0, y0) to any point of the parabola.

 2. Then, you have:

 √(x0-a)^2+(y0-b)^[2=|y0-10|

 3. When you susbtitute values and simplify it, you obtain:

 (√(x0-4)^2+(y0-0)^2)^2=(y0-10)^2
 (x0-4)^2+y0^2=(y0-10)^2
 

 4. Now, you must clear y, and you will have:

 y=(-x^2/20)+(2x/5)+(21/5)