196 Part 3: The Shape of the World
The Least You Need to Know
- Parallelograms have both pairs of opposite sides parallel. Area formula: A = bh.
- Rhombuses are parallelograms with four equal sides. Area formula: A = the prod-
uct of the diagonals divided by 2. - Rectangles are parallelograms with four right angles. Area: A = lw. Squares are
rectangles that are also rhombuses. Area formula: A = s^2. - Trapezoids are quadrilaterals with one pair of parallel sides. Isosceles trapezoids
have nonparallel sides congruent and base angles congruent. Area formula:
A = 21 h multiplied by the sum of the bases. - Regular polygons have congruent sides and congruent angles.
- Total of the interior angles of a polygon with n sides is 180(n – 2).
CHECK POINT- Find the area of a regular pentagon with sides 8 cm long and an apothem 5 cm
long. - Find the area of an octagon with a perimeter of 40 inches and an apothem of
5 inches. - Find the area of a regular decagon if each of the 10 sides measures 2 meters and
the apothem is 1.5 meters. - The perimeter of a regular hexagon is 42 inches and its area is 84 square inches.
How long is its apothem? - A regular pentagon has an area of 1,080 square inches and an apothem of
18 inches. How long is each side?