Question

Derive the equation of the parabola with a focus at (2, 4) and a directrix of y = 8.

Answer 1

f(x) = −one eighth (x − 2)^2 + 6

f(x) = one eighth (x − 2)^2 + 6

f(x) = −one eighth (x + 2)^2 + 8

f(x) = one eighth (x + 2)^2 + 8

Answer 2

first example here will explain
http://www.purplemath.com/modules/parabola3.htm