SYMMETRY

What is Symmetry?

A figure is Symmetric (or symmetrical) if it can be divided into two congruent parts by a line known as the axis of symmetry. This line acts like a mirror, so an axis of symmetry is really an axis of reflection. A figure with no symmetry is called asymmetric (or asymmetrical).

We can see the line of symmetry in this image. It's the surface of the water under the bridge.

Our world is full of symmetric images as we see in these natural shapes and patterns.

An axis of symmetry is often called a fold line. If these images were on paper, we could fold them to create a crease that would be the line or axis of symmetry because the two sides of the image would match perfectly. In all these images, the axis of symmetry is vertical. But they need not be.

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This image has many lines of symmetry, now doesn't it?
We could fold it many ways and have symmetry.

Any diameter shown on the wheel can serve as an axis of symmetry or fold line.

Example: How many lines of symmetry are there for each figure shown?

Letters, numbers and words can be symmetrical too.

Now get a pencil, an eraser and a note book with graph paper, copy the questions,
do the practice exercise(s),then check your work with the solutions.
If you get stuck, review the examples in the lesson, then try again.

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Practice

1) Is the red line an axis of symmetry? Write yes or no.

2) On graph paper, copy and complete these images to make the red line an axis of symmetry.

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Solutions

1)
 a) no b) yes c) yes d) no

2)