00:01
Okay, so we want to use the definition of the derivative to find it, and that definition is, just for a reminder, the limit as h approaches zero of the function of x plus h minus the function at x over h.
00:23
And the function we will be working with is f of x is equal to x squared minus 2x cubed.
00:34
So that means that the function at x plus h will be x plus h squared minus 2 times x plus h cubed.
00:48
Okay, so if we distribute everything, this is going to be equal to x squared plus 2xh plus h squared.
01:00
Then now we're going to start subtracting, right? so that's going to be minus 2x cubed.
01:08
Minus 6x squared h minus 6x h squared minus 6x h squared minus 2h cubed okay so we can put both of these into our definition so that means that this is going to be equal to the limit as h approaches zero of x squared plus 2x h plus h squared minus 2xh cubed minus 6x squared, h minus 6x squared, h squared minus 2 h cubed.
01:57
Then we need to subtract the f of x.
02:03
Okay, so then, so it be minus x squared and minus 2x cubes.
02:10
I'll draw a little line here to kind of separate that.
02:15
And this will be all over h.
02:18
Well, we get some cancellations when we do this, right? so actually the ipod is this last one, this minus 2x cubed being subtracted should be added together...