Lesson 5

The purpose of this lesson is for students to identify figures with line symmetry and to complete line-symmetric figures.

Previously, students learned to identify figures with line symmetry and drew lines of symmetry. In this lesson, students deepen their understanding of symmetry by reasoning about what the whole figure would look like when given half of a figure and a line of symmetry.

The work of this lesson helps students develop mental images of figures with lines of symmetry. Students also consider how to use what they know about drawing line segments, points, and angles to complete their drawings. They make strategic decisions about how to use available tools to complete the shapes or justify how they know their figures are symmetrical (MP5). Students may copy the figure to another piece of paper, and follow with folding, cutting, or tracing. They may also use rulers or protractors to measure distances and angles.

• Create a set of triangle cutouts from the blackline master for each group of 2.

What connections did students make between the different strategies shared? What questions did you ask to help make the connections more visible?