Question

What is the equation of a parabola with a vertex at (0, 0) and a directrix x = -4?

Answer 1

The general form for this is  y^2 = 4ax   where a = focus

the directrix is same distabce behind the vertex as focus is in font so focus   a = 4

so we have y^2 = 16 x 
or 
x = (1/16) y^2

Its  C