TOPIC 5 · GRADE 3 FOUNDATION

Lines of Symmetry

Find lines that divide a figure into matching mirror halves.

MA.3.GR.1.3

BIG IDEA

A line of symmetry is a fold line: if the figure folds there, corresponding edges and points match exactly.

WHAT TO KNOW

A figure may have no symmetry, exactly one line, or several lines of symmetry.
A rectangle has two lines of symmetry, while a non-square rhombus has two different diagonal lines.
Orientation does not change the number of symmetry lines.

WATCH OUT

A line through the center is not always a symmetry line; the two halves must be mirror images.

TRY IT

Choose a figure and turn possible fold lines on and off.

Choose the next topic from the lesson rail when you are ready.