# Lesson 15 — Activity 2: Estimating and Calculating the Area of Quadrilaterals

#### You may have learned in previous courses about polygons. A polygon is any closed two-dimensional shape that has three or more straight sides. A triangle has three sides, so it is a polygon. A rectangle has 4 sides, so it is a polygon too. There are also four-sided shapes other than a rectangle that are polygons. These shapes are called quadrilaterals. In this activity, you will learn how to calculate the area of two quadrilaterals: squares and parallelograms. #### A square is a four-sided shape where all the sides are the same length. Each corner is a right angle. #### Units of measurement are called square units. Four dots make a square. #### unit × unit = units2 Count the number of squares that can be made inside the shape. #### A parallelogram is a two-dimensional shape with four line segments, or sides, with opposite pairs of sides parallel and equal in length. #### The area of a parallelogram can be estimated using a variety of methods. One method is to use grid paper. #### Estimate the area of the parallelogram labeled D below. You can prove your answer by using the geoboard once again. Remember to first count the whole squares and then combine the partial squares. Image of parallelogram courtesy of © 2008 National Council of Teachers of Mathematics
http://illuminations.nctm.org

#### Using this square #### Using this parallelogram #### A = b x h A = 54 x 10 A = 540 km2

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