00:01
Okay, we have f of x is equal x plus 3x to the two thirds.
00:04
We're working on the interval negative 10 to 1.
00:06
We need to find any absolute extrema for this function.
00:11
Step 1, we need to find the derivative.
00:13
If you're not familiar with the steps, feel free to go back and look at the other videos.
00:18
F prime of x, just taking the derivative, is equal to 1 plus.
00:24
We bring down the 2 thirds.
00:26
So we're going to get 2x.
00:29
You have to subtract one from your exponent when you take derivative so this leaves us with x to the negative one -third to clean this up a little bit we're going to rewrite it as one plus two over the cubed root of x and this needs to be equal to zero so so with this equal to zero, we know we're going to have a couple different ways to do that.
01:04
It might be easier to go ahead and find a common denominator here, so let's do that.
01:08
So we're going to have three square root of x plus two over three square root of x is equal to zero.
01:19
So to get to from here to here, find common denominator.
01:36
Denominator.
01:39
Okay, so that's how we got from there to there.
01:41
So now we're going to take this, solve it for zero.
01:45
That leaves us with third root of x plus two equals zero, which means when we solve this, we're going to have third root of x is equal to negative two.
02:01
I'm going to go over to the next page.
02:04
We have three, three, cubed root x.
02:13
Is equal to negative 2.
02:16
And now you have to get rid of this cubed root of x.
02:19
This is the same thing as x to the 1 3rd.
02:24
So to get rid of this, to get rid of a 1 3rd cube, we're going to cube.
02:34
We're going to cube.
02:36
Because when we cube it, we get 3 over 3, which is 1.
02:42
So we end up with x equal to negative 2 cubed, which is negative.
02:49
8.
02:51
Okay, so we have this as a regular critical point.
02:57
We also need to check and see where our derivative is undefined.
03:02
So that's the other question you need to ask yourself.
03:06
Where is f prime of x undefined? and is that in my interval? so let's just see if we even have any spaces to worry about...