00:01
Here i'll be looking at the relationship between a riemann sum and a definite integral.
00:07
But recall that both of these are trying to find the area under a curve.
00:14
So i'll draw a curve, f of x is a function of x, and we're going from point a to point b under that curve.
00:24
So that's what we mean by a definite integral.
00:28
But the riemann sum breaks up the interval into a set of n pieces, and i'll just show four pieces.
00:39
And then you make rectangles based on the base being a finite thickness and the height coming from the function itself.
00:53
And i'm using right endpoints there to evaluate the function.
00:57
So the rhyme -on sum in this case would be delta x times the summation of f of x -i -i equal 1 -4.
01:16
And i'll just show where those x -es are, x -1, x2, x -3, and x -4.
01:26
So to begin with, i'm going to show kind of a general way to write that rhyme -on -sum, based on a general breaking up the interval a to b into n pieces.
01:44
Okay.
01:45
So we're going to take a look at more in general, more generally.
01:50
So we're taking the x axis and we start at a and we start at b.
01:57
And delta x is simply taking the difference between the two end points and dividing into n pieces.
02:07
Okay, so all the way out.
02:11
Now, the first position, we'll call that x1, starts at a, but then you've added a little delta x to that.
02:22
And then x2 is equal to a plus 2 delta x, etc.
02:34
And so you can write in general that x of i is equal to a plus i times delta x...