00:01
F of x is equal to x cubed minus 3x.
00:07
And we want to find f prime of x first of all.
00:10
So that's going to be limit h tends to 0, f of x plus h minus f of x over h.
00:21
And that would be limit h tends to zero, x plus h to the power 3 minus three times x plus h minus x cubed minus three x over h so limit h tends to zero we want to use the bimonial expansion here so that would be x to the power three plus three x squared h plus three x squared and then minus the plus h cubed and then minus 3x minus 3h and then minus x cubed and then minus x cubed minus 3x so first thing we can do is we can simplify things here a little bit so x cube minus x cube and then minus 3x and then this should be plus 3x so they cancel us now for the remaining terms, what we find is that each term has an h in it in the numerator.
01:34
So let's just factor that h out.
01:37
So we're going to say h times 3x squared plus 3xh minus h squared minus 3 and then divided by h.
01:50
So the h in the numerator and the h in the denominator cross out.
01:55
And then we can now actually say that h is equal to 0.
02:00
We can substitute that, and when we do substitute that, we get 3x squared minus 3.
02:07
So that's the first derivative of the function.
02:11
Now, the question says also to find the second derivative...