How do you write an equation for the parabola with vertex (-1,2) and directrix x=-2?
We need to know the value of
Since the vertex is the same distance from both the focus and the directrix, we don't need to know the focus. The vertex is at the x-value of
Before we go any further, we should know that the directrix is always outside of the parabola. Since it's a vertical line and is to the left of the parabola, the graph opens to the right. Here's the standard form for a right-facing parabola:
We can use this to find our scale factor. We know that