A Reimann sum is an illustration of what an integral is. It is the area of an
infinite number of rectangles under the graph. Thus, giving the area.
If we come off of the right side of the rectangles, we can use
In this case, each subinterval has length
So, we get
Giving the area of rectangle k as
The sum of the area of all these rectangles is
But we know from some identities that
We sub these is and take the limit as n-->infinity. This means the number of rectangles becomes larger and larger and we approach the area under the curve.
Doing all this algebra we get:
Which is the value of the integral