I'm having problems on this lesson. Can someone please help me understand it?

Question

anonymous · Answer

Find the standard form of the equation of the parabola with a focus at (-4, 0) and a directrix at x = 4.

anonymous · Answer

I found the vertex (0,0)

anonymous · Answer

yes

anonymous · Answer

but i need to form the whole equation

anonymous · Answer

|dw:1406514170440:dw|

anonymous · Answer

you can see that it opens to the left so the y is squared not the x

anonymous · Answer

how do i know it opens to the left.. there's no p

anonymous · Answer

look at the picture of the focus and directrix

anonymous · Answer

ohhh yes the directrix is always on the curve?

anonymous · Answer

all points equidistant from those two
you already found the vertex at $(0,0)$ so you must realize what the picture looks like right?

anonymous · Answer

no the directrix is a line, never on the curve

anonymous · Answer

yes but it's the line beside the curve?

anonymous · Answer

|dw:1406514387537:dw|

anonymous · Answer

|dw:1406514430990:dw|