00:01
All right, hello, in this question we're given this function f of x equals 4x minus 5 arc tangent of x, and on the interval negative 2 root 3 to 2 root 3, we want to find the absolute max and min, but first we want to go ahead and find our critical points.
00:12
So a is find the critical points of this function.
00:14
In order to do that we need to take a derivative, and that derivative is going to be 4 minus 5 times the derivative of arc tangent of x, which is 1 over 1 plus x squared, and then i want to set that equal to 0 and solve.
00:30
So i can move this term to the right side to make it positive and then cross multiply, so i'll get 4 plus 4x squared equals 5.
00:38
So x is going to be plus or minus the square root of 1 over 4, which is going to be plus or minus one half.
00:47
Both of those fall within our domain of interest, so those will both be good candidates for our critical points.
00:53
We're asking part b to use a first derivative test to identify if these are maxes or mins, so we're going to look at different values of x here.
01:01
I don't need to look at these endpoints because i just want to consider those for absolute max and min, but for as far as the sign goes i can look from negative infinity to negative one half, and then between those two critical points, and then from one half to infinity, and i want to see what the sign of f prime is going to be.
01:23
So this function here, if i plug in a very large negative number, this term is going to get very big, and so this term is essentially going to go to 0.
01:32
So i'm going to have 4 minus 0, it's going to be 4, that's going to be a positive value.
01:36
0 lies within there, so i can just plug in 0, and if i do that i'm going to get 4 minus 5, which is negative 1, so that's going to be negative.
01:42
And then again if i plug in a very large number, this term goes to 0, and so i'll get 4, which is a positive number...