00:01
Let's take a look at the parabola, y equals negative 1 half x squared minus x plus 1.
00:09
If we look at the x squared term, we see that it has a negative coefficient, which means this parabola opens downward.
00:17
We have two options for that parabola, either a or c.
00:22
To narrow it down between those two, let's find where the vertex is, and we'll compare that with the pictures of the two parabolas a and c.
00:30
To find the vertex, we complete the square.
00:35
Every term with an x, we're going to group together.
00:38
Terms without the x, we're going to push over to the side, in this case plus 1.
00:43
X squared needs to have a coefficient of 1, so i'm going to factor out a negative 1 half from every term that has an x in it.
00:55
And i'm going to leave some space inside my parentheses.
01:00
To complete the square, we look at the coefficient of the x term.
01:04
We take half of it, in this case 1, and square it...