# Rotations

A rotation is a
transformation
in a plane that turns every point of a preimage through a specified angle and direction about a fixed point. The fixed point is called the
center of rotation
. The amount of rotation is called the angle of rotation and it is measured in degrees. Use a
*
protractor
*
to measure the specified angle counterclockwise.

Some simple rotations can be performed easily in the coordinate plane using the rules below.

### Rotation by $90\xb0$ about the origin:

A rotation by $90\xb0$ about the origin is shown.

The rule for a rotation by $90\xb0$ about the origin is $(x,y)\to (-y,x)$ .

### Rotation by $180\xb0$ about the origin:

A rotation by $180\xb0$ about the origin is shown.

The rule for a rotation by $180\xb0$ about the origin is $(x,y)\to (-x,-y)$ .

### Rotation by $270\xb0$ about the origin:

A rotation by $270\xb0$ about the origin is shown.

The rule for a rotation by $270\xb0$ about the origin is $(x,y)\to (y,-x)$ .