# Transformations and SymmetryRigid Transformations

A **rigid transformation**

Which of these five transformations are rigid?

It turns out that there are just three different types of rigid transformations:

A transformation that simply *moves* a shape is called a **translation**

A transformation that *flips* a shape over is called a **reflection**

A transformation that *spins* a shape is called a **rotation**

We can also combine multiple types of transformation to create more complex ones – for example, a translation followed by a rotation.

But first, let’s have a look at each of these types of transformations in more detail.

## Translations

A **translation**

In the coordinate plane, we can specify a translation by how far the shape is moved along the *x*-axis and the *y*-axis. For example, a transformation by (3, 5) moves a shape by 3 along the *x*-axis and by 5 along the *y*-axis.

Now it’s your turn – translate the following shapes as shown:

## Reflections

A **reflection****line of reflection**.

Draw the line of reflection in each of these examples:

Now it’s your turn – draw the reflection of each of these shapes:

Notice that if a point lies on the line of reflection, it

In all of the examples above, the line of reflection was horizontal, vertical, or at a 45° angle – which made it easy to draw the reflections. If that is not the case, the construction requires a bit more work:

To reflect this shape across the line of reflection, we have to reflect every

Let’s pick one of the vertices and draw the line through this vertex that is perpendicular to the line of reflection.

Now we can measure the distance from the vertex to the line of the reflection, and make the point that has the same distance on the other side. (We can either use a ruler or a compass to do this.)

We can do the same for all the other vertices of our shape.

Now we just have to connect the reflected vertices in the correct order, and we’ve found the reflection!

## Rotations

A **rotation****center of rotation**

Try to rotate the shapes below around the red center of rotation:

It is more difficult to draw rotations that are not exactly 90° or 180°. Let's try to rotate this shape by

Like for reflections, we have to rotate every point in a shape individually.

We start by picking one of the vertices and drawing a line to the center of rotation.

Using a protractor, we can measure an angle of ${ang*10}° around the center of rotation. Let’s draw a second line at that angle.

Using a compass or ruler, we can find a point on this line that has the same distance from the center of rotation as the original point.

Now we have to repeat these steps for all other vertices of our shape.

And finally, like before, we can connect the individual vertices to get the rotated image of our original shape.

Transformations are an important concept in many parts of mathematics, not just geometry. For example, you can transform *functions*