00:01
So our parabola is x squared plus 2x minus 8.
00:06
So we have a trinomial now and let's factor that.
00:09
And i can see that x and x and a 4 and a 2.
00:13
And i need a positive middle term.
00:15
And that multiplication will give me the appropriate multiplication to give that trinomial.
00:21
So we want to give what the, we know it opens upward because of that positive coefficient.
00:26
And we know that we want to find the vertex axis of.
00:30
Symmetry we want to know what the x intercepts are which let's write those down we can see those are occurring at negative four and two and we want to know what the y intercept is and let's go back to this if we plug zero in place of x here zero zero we're going to end up getting negative eight so i can see my y intercept is down at negative eight now my vertex is going to be halfway between these two so if we add them together and divide by two a negative four plus two divided by 2 gives me, excuse me, negative 2 over 1 over 2.
01:05
So i'm going to have negative 1 as my middle.
01:07
So i know my vertex is at negative 1 and something.
01:12
And our axis of symmetry is x equals negative 1.
01:15
So let's plug in negative 1 and find out what we get here.
01:20
If we plug in negative 1, we'll get 1.
01:22
And then we'll get plus and plug negative 1 in there.
01:25
We get negative 2 plus 8.
01:27
So these two combined to give me negative 1.
01:29
So it looks like seven.
01:31
So it looks like our vertex is at negative 1 and 7.
01:34
So let's get our graph.
01:37
And we'll get a little axis system here.
01:40
We know i need to go as low as negative 8.
01:43
And for the y, the y intercept.
01:47
And our vertex is at negative 1 and 7.
01:51
So let's get our little graph here.
01:56
Okay.
01:58
So we have one, two, three, four, five.
02:02
Negative 5 this way, 1, 2, 3, 4, 5 this way.
02:06
We know that we're going to have a 0 at negative 4 and at 2.
02:12
We know our axis of symmetry is going to take place right there at x equals negative 1.
02:17
We know we're going to have a y intercept down here at negative 8, and our vertex is going to be at negative 1, 7.
02:24
Negative 1 and 7.
02:28
Oh, and i made a mistake.
02:30
And you caught that.
02:31
This is a subtraction sign right here...