# Riemann Sum

Riemann Sum is a method for approximating the area underneath a continuous function. To find the Riemann’s sum, divide the area under the curve into *n* equal width rectangles. Then calculate the area of each rectangle and sum the results together. This is described by the equation below:

The variable **A** represents the approximated area, **f(x _{i})** represents the height of each rectangle and

**dx**(the change in x), represents the width of each rectangle. The symbol Σ means add all of the parts together.

Note: This image shows the left approximation method, see the interactive above for the alternative methods: mid-point, right, and trapezoid.

## Examples

### Riemann Sum of Function Left Approximation

To calculate the Riemann sum of a function using the left approximation method. negative x squared plus four x from zero to four using the left approximation method.