00:03
We want to start by first finding the coordinates of any critical points and classifying those points as relative min or max or neither.
00:12
So we're going to take the derivative of this function, which gives me 15x squared minus 15.
00:20
We're going to set that function equal to zero.
00:25
I'm going to factor out 15.
00:30
That's going to give me x plus 1, x minus 1.
00:33
So my critical points are going to be at negative 1 and 1.
00:44
I can get the corresponding y coordinates by just plugging in those values.
00:49
If i plug in negative 1, i'm going to get out positive 10.
00:53
If i put in positive 1, i'm going to get out negative 10.
00:58
Now i want to be able to classify those as min or max points.
01:02
I plot them on a number line.
01:08
I'm going to choose values to the left and right, and i'm going to test those values in my first derivative.
01:16
So i want f prime of negative 2, f prime of 0, and f prime of positive 2.
01:22
I don't really care what number comes out.
01:25
I care whether it's positive or negative.
01:27
So f prime of negative 2 is going to give me 4 times 15, which is 60 minus 15, that's a positive.
01:36
I'm going to get the same result putting in positive 2.
01:40
If i put in 0, i get out negative 15, which is negative.
01:45
So that gives me these results.
01:47
Positive, negative, positive.
01:50
So that tells me my graph is increasing, decreasing, and then increasing.
01:56
So at negative 1 .10, i'm going to have a relative maximum.
02:07
At positive 1, negative 10, i'm going to have a relative maximum.
02:10
A relative minimum...