Area of a Trapezoid

Use this dynamic worksheet to derive the formula for area of a trapezoid.
Use the slider to rotate the trapezoid around BD. 1. What shape do the two combined trapezoids form? 2. Let b1 represent the length of AB and b2 represent the length of CD. What is the length of the base of the shape formed by the combined trapezoids. 3. Write a formula for the area of the combined shape in terms of b1, b2, and h. 4. Write a formula for the area of a single trapezoid in terms of b1, b2, and h.