00:01
Before we begin, we could confirm that the graph of ln of x is continuous and differentiable from 1 to 4.
00:10
So we're good on the conditions.
00:12
And then we'll go ahead and set up what the slope of the secant line is, f of 4 minus f of 1, all over 4 minus 1.
00:26
And that, in other words, would be what the slope is connecting these two points, that secant line.
00:38
And let's see, we'll end up getting f of 1 is 0, and the bottom that's the same thing as 3.
00:49
So really, on the left side there, we'll end up with ln of 4 over 3.
00:58
And that's that secan slope.
01:02
On the right hand side, we want to find out when this is equal to what c value does the tangent line have the same slope? in other words, what is the c for f prime to have that? and so taking the derivative, this is going to get us 1 over x, a derivative of that line of x.
01:23
And then just cross multiplying here, or taking the reciprocal of both sides...