Trapezoidal rule

The trapezoidal rule is a way of figuring out the area of a shape, like a rectangle or triangle. First, draw a line across the shape. We call this a "base line". Then, draw lines from one corner of the shape to the other side, like stairs going up the shape. These lines are called "trapezoids" because they look like trapezoids (shapes with four sides, two of which are parallel). To figure out the area of this shape, add up the area of each trapezoid. The formula for the area of a single trapezoid is (height x length of the base line) + (height x length of the top line) / 2. So, if the shape has four trapezoids, you would use the trapezoidal rule to calculate the total area of the shape like this:

(height of first trapezoid x length of base line) + (height of first trapezoid x length of top line) +
(height of second trapezoid x length of base line) + (height of second trapezoid x length of top line) +
(height of third trapezoid x length of base line) + (height of third trapezoid x length of top line) +
(height of fourth trapezoid x length of base line) + (height of fourth trapezoid x length of top line)

all divided by 2.