# What is the vertex form of #y= x^2 - 10x - 9 #?

##### 1 Answer

Apr 19, 2018

First, we need to complete the square

What would make

As a perfect square:

Now let's look at our original equation.

**NOTE that we subtracted #25# after we added it. That's because we added #25#, but as long as we later subtract it, we haven't changed the value of the expression**

To check our work, let's graph our original function and what we have. If we did it right, they should be the same

graph{y=x^2+10x-9}

graph{y=(x+5)^2-34}

Looks like we were right!