Question 633490
Standard form of parabola: (y-k)^2=-4p(x-h), with (h,k) being the (x,y) coordinates 
of the vertex. This parabola opens leftwards and has a horizontal axis of symmetry.

For given problem:

Axis of symmetry = x-axis or y=0

p=distance from vertex to focus on axis of symmetry=4
center (0, 0) 

Equation:

{{{y^2=-16x }}}

See graph below as a visual check on the equation



{{{ graph( 300, 300, -10, 10, -10, 10,(-16x)^.5,-(-16x)^.5) }}}