00:01
Ok, in this exercise we have our function f ' of x equal to 2 multiplied by 1 minus x squared over 1 plus x squared.
00:14
Now, before we go on, let's draw a sine chart for f'.
00:20
So this is going to be sine of f'.
00:23
Well, we know that f ' is going to be positive between negative 1 and 1 and negative on the complement, so for x less than negative 1 and x greater than 1.
00:40
Perfect.
00:41
So, this sine chart here tells us that f is increasing on the interval negative 1, 1 decreasing on the union of the intervals negative infinity, negative 1 and 1, infinity.
01:06
Moreover, f has a local minimum at negative 1, at x equal to negative 1 and a local maximum at x equal to 1.
01:24
Perfect.
01:24
Now, let's take a look at the second derivative.
01:29
Well, the second derivative is 4x multiplied by x squared minus 3 over 1 plus x squared squared.
01:41
Now, let's draw a sine chart for f'.
01:44
So this is sine of f'.
01:49
Okay, here we can see that we have three zeros of f'.
01:56
X equal to 0, x equal to negative square root of 3 and x equal to square root of 3...