# What is the vertex form of the equation of the parabola with a focus at (200,-150) and a directrix of #y=135 #?

##### 1 Answer

Nov 22, 2015

The **directrix** is above the **focus** , so this is a parabola that **opens downward** .

#### Explanation:

The **x-coordinate** of the focus is also the x-coordinate of the **vertex** . So, we know that

Now, the **y-coordinate** of the **vertex** is *halfway* between the directrix and the focus:

**vertex**

The distance

**Vertex form** :

Inserting the values from above into the vertex form and remember that this is **downward opening** parabola so the sign is **negative** :

Hope that helped