00:01
Okay, let's start with the first derivative.
00:03
4x cubed minus 64x is equal to zero.
00:09
Take 4x out.
00:11
X squared minus 64.
00:17
Wait a second, that's not 64, 16.
00:20
This is 16.
00:24
So x equals zero, x equals four, and x equals negative four are the critical points.
00:34
Negative infinity f prime.
00:37
So negative four and zero and four and infinity.
00:51
Okay, so let's put negative five for the first derivative.
00:56
You get 25 minus 9 positive negative and then put negative 2.
01:03
Negative, negative, positive.
01:08
What about 1? positive, negative, 5, positive, positive.
01:13
So decreasing, increasing, decreasing, increasing.
01:18
Okay, increasing from negative four to zero.
01:29
Union four to infinity and decreasing from negative infinity to negative four.
01:40
Union zero to four.
01:46
And then here is a local min, local max, and then the local min.
01:52
So local min, minimum, at plus or minus 4 comma negative 248.
02:04
And local max at 0 comma 8.
02:10
Okay, second derivative.
02:14
Second derivative is 12x squared minus 64...