Let us recall that a trapezoid is a quadrilateral that has exactly one pair of sides parallel. The area formula for trapezoids is based on the area formulas that have been previously derived and discussed. Now let us do the following steps to derive the area formula for trapezoids.
- Draw a trapezoid ABCD and label its bases as and , respectively.
- Fold it so that the bases meet.
- Cut along this folded line, which is actually the median of the trapezoid.
- Label the height of each piece with since the original height of the trapezoid is now being cut into two equal heights.
- Rotate the top half part clockwise so that and are on the same line.
Therefore, the area of the trapezoid above is equal to the area of the parallelogram formed below. Using the area formula for parallelogram, we have
Area Formula for Trapezoid
where and are the bases and is the height of the trapezoid.
1. The height of the trapezoid is unknown, so we solve for using the Pythagorean Theorem.
2. The height of the trapezoid is unknown, so we solve for using the Pythagorean Theorem. The shorter leg of the triangle formed with the altitude and the leg of the trapezoid is equal to 1 unit, that is .
3. All the necessary parts used to solve for the area of the trapezoid are known, so the area of the trapezoid is