Session 7, Part A:
Line Symmetry (30 minutes)

In This Part: Finding Lines of Symmetry | The Perpendicular Bisector

 In Session 5, you saw three ways to move figures around: rotation, reflection, and translation. If you can move an entire design in one of these ways, and that design appears unchanged, then the design is symmetric. If you can reflect (or flip) a figure over a line and the figure appears unchanged, then the figure has reflection symmetry or line symmetry. The line that you reflect over is called the line of symmetry. A line of symmetry divides a figure into two mirror-image halves. The dashed lines below are lines of symmetry: The dashed lines below are not lines of symmetry. Though they do cut the figures in half, they don't create mirror-image halves. You can use a Mira (image reflector) or simply the process of cutting and folding to find lines of symmetry. Print the PDF version of the figures above, and compare the lines proposed using a Mira. In Problems A1 and A2, sketch the figures or print the PDF files of the figures and show the lines of symmetry as dashed lines. Problem A1 For each figure, find all the lines of symmetry you can.

 Problem A2 Find all the lines of symmetry for these regular polygons. Generalize a rule about the number of lines of symmetry for regular polygons.

 Part A: Finding Lines of Symmetry adapted from IMPACT Mathematics, Course 3, developed by Educational Development Center, Inc. pp. 289-290. © 2000 Glencoe/McGraw-Hill. Used with permission. www.glencoe.com/sec/math Problems A1 and A2 adapted from IMPACT Mathematics, Course 3, developed by Educational Development Center, Inc. pp. 290-291. © 2000 Glencoe/McGraw-Hill. Used with permission. www.glencoe.com/sec/math
 Session 7: Index | Notes | Solutions | Video