To fi nd the perimeter of a trapezoid, we add the lengths of the four sides. To fi nd the area of a trapezoid, use this formula: Formula Area of a Trapezoid The area, A, of a trapezoid is A 1 2 height (short base long base) or A 1 2 h(b B) or short base, b height, h long base, B where h the height, b the length of the short base, and B the length of the long base. The bases are always the parallel sides. Find the a) perimeter and b) area of the trapezoid. 13 in. 3 13 in. 3 4 in. 5 in. 25 in. 3 Solution a) Perimeter: The perimeter is the distance around the fi gure, so add the lengths of the sides. (Do not add the 4 in. because it is the height of the trapezoid and not a side.) P 5 in. 13 3 in. 25 3 in. 13 3 in. P 15 3 in. 13 3 in. 25 3 in. 13 3 in. Get a common denominator. P 66 3 in. or 22 in. Add and simplify. The perimeter of the trapezoid is 22 in. b) Area: Use the formula: A 1 2 h (b B) where h height, b short base, and B long base. Identify h, b, and B. The bases are the parallel sides. h 4 in. b 5 in. B 25 3 in. aWe do not need either of the 13 3 in. sides.b EXAMPLE 6 www.mhhe.com/messersmith SECTION 4.2 Rectangles, Squares, Parallelograms, and Trapezoids 301
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