00:01
We're looking at a tangent line problem.
00:03
And with a tangent line, what we need is a point and a slope.
00:09
And they generously tell us the point is at negative 2, negative 10.
00:16
And in order to find the slope, what we need to do is find the derivative and plug in the x coordinate negative 2 into the derivative.
00:26
And they also tell us that f of x is equal to 3x minus x squared.
00:33
So the first thing that we need to do, since we're doing the limit definition of the directive, is figure out what f of x plus h is.
00:44
So i need to replace all of those x's in the equation with x plus h.
00:50
And when i start to distribute as well as folio, because remember x plus h squared means x plus h times x plus h.
01:01
And while i'm added, i also need to distribute that negative into that.
01:07
So there would be 2xh and then also an h squared that would become negative.
01:13
So when i go to find the limit as h approaches zero of f of x plus h minus the difference of those two, what you'll notice is the 3x minus 3x will cancel, and then the negative x squared minus a negative x squared.
01:30
Will cancel.
01:32
And what i can do is factor out an h between the 3, the minus 2x, and the minus h.
01:39
And that way, i could cancel out the h's.
01:43
By the way, this is the definition of f prime of x is what i'm doing.
01:47
And now i can plug in zero for this, for the h value, i'm left with 3 minus 2x...