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May 2013

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The ideas in this geometry lesson are taken from Math Mammoth Geometry 1 book that I sell at MathMammoth.com. This lesson plan does not contain all the problems included in the Geometry book.

Line Symmetry
Free geometry lesson plan from HomeschoolMath.net

These figures are symmetrical in relation to the dashed line. The line is called a symmetry line. This means that one half of the figure is the mirror image of the other half.                Imagine that you folded the figure along the symmetry line.  Then both sides would exactly meet. Or, place a mirror along the symmetry line. You see the other half of the figure reflected in the mirror.
Some shapes you can fold two different ways so that the sides meet. The cross-shape on the right has two different symmetry lines.
Look at this flower shape. It has four different symmetry lines. Check them by using the mirror.
Any line that you draw through the circle's center point is a symmetry line. So, we can't even count how many symmetry lines a circle has! Draw you one more example in the last circle.
Some shapes have only one symmetry line, like this arrow shape.	Many figures are not symmetrical at all.

1. Are these figures symmetrical? Draw a symmetry line to those that are.
    You can also cut them out and fold them to check.

a.

b.

c.

d.

e.

The case of the parallelogram Does a parallelogram have a symmetry line like this? Use a mirror to check! Or, draw a parallelogram, cut it out, and fold it along the diagonal line. Do the two folded sides match?

Here's the answer: The red dotted line shows you how the folding would go. The two sides don't match, so the blue dashed line is NOT a symmetry line.

2. Is the line drawn a symmetry line for the figure?

a.

b.

c.

d.

e.

f.

3. Draw different symmetry lines to these figures.

a.

b.

c.

d.

4. Write the capital letters to which you can draw a symmetry line. Draw the symmetry lines to them.

Next geometry lesson