Trapezoid
Grade 8 math lesson on trapezoids including properties, area formulas, and identification. Students learn that a trapezoid has exactly one pair of parallel sides called bases, and practice calculating trapezoid area using the formula (base1 + base2) / 2 times height.
Key Concepts
Property A quadrilateral with one pair of parallel sides is a trapezoid.
Examples In a trapezoid, the two parallel bases can have lengths of 5 cm and 10 cm, while the non parallel legs can be 6 cm and 7 cm. An isosceles trapezoid has one pair of parallel sides and its non parallel sides are equal in length. Figure E from the lesson is a trapezoid because it has exactly one pair of parallel sides.
Explanation This shape is all about having just one set of parallel sides, called bases. Think of it as a quadrilateral that couldn't fully commit to being a parallelogram. The other two sides, the legs, are not parallel and can be different lengths. If the legs happen to be equal, you have a special, more symmetrical version called an isosceles trapezoid.
Common Questions
What is a trapezoid?
A trapezoid is a quadrilateral (four-sided polygon) with exactly one pair of parallel sides. The parallel sides are called bases, and the non-parallel sides are called legs. An isosceles trapezoid has equal-length legs.
How do you calculate the area of a trapezoid?
The area of a trapezoid = (base1 + base2) / 2 times height. Add the two parallel bases, divide by 2 to get the average base length, then multiply by the height (perpendicular distance between the bases).
How is a trapezoid different from a parallelogram?
A parallelogram has two pairs of parallel sides, while a trapezoid has exactly one pair. A parallelogram area is simply base times height, while a trapezoid formula must account for two different-length parallel sides.
What are the bases and legs of a trapezoid?
The two parallel sides of a trapezoid are called bases (usually labeled b1 and b2). The two non-parallel sides are called legs. The height is the perpendicular distance between the two bases.