Description
write an equation for the parabola whose focus is (0,2) and whose directrix is x=2

Explanation & Answer

Vertex is the mid point between focus and directrix.
=> Vertex = ( 1, 2 ).
Because the focus is on the left of the vertex, the parabola opens on the left.
General equation is this case is :
( y - k ) ^2 = 4a ( x - h ).
Where (h ,k) is the vertex.
|a| is the distance between focus and vertex = 1
Because parabola faces left, a = -1.
=> Equation is :
( y - 2 )^2 = -4 ( x - 1 )
