As we get further into geometry, we will learn many different techniques for transforming graphs. One of these techniques is "rotation." As we might have guessed, this involves turning a figure around on its axis. But how exactly does this work? Let's find out:
What is a rotation?
We're probably already familiar with the concept of rotation. After all, the wheels on a bicycle or a skateboard rotate. We can even rotate ourselves by spinning around until we get dizzy. As it turns out, the mathematical definition of rotation isn't all that different. Just like the wheel on a bicycle, a figure on a graph rotates around its axis or "center of rotation."
We measure the "amount" of rotation in degrees, and we can do this manually using a protractor. On the other hand, we can also use certain calculations to determine the amount of rotation even without graphing our points.
Visualizing the rules of rotation
There are many important rules when it comes to rotation. Some of the most useful rules to memorize are the transformations of common angles. Let's start with everyone's favorite: The right, 90-degree angle:
As we can see, we have transformed P by rotating it 90 degrees. We might have noticed a pattern: The values are reversed, with the y value on the rotated point becoming negative. In other words:
With a 90-degree rotation around the origin, (x,y) becomes (-y,x)
Now let's consider a 180-degree rotation:
We can see another predictable pattern here. When we rotate a point around the origin by 180 degrees, the rule is as follows:
(x,y) becomes (-x,-y)
Now let's consider a 270-degree rotation:
Can you spot the pattern? The general rule here is as follows:
When rotating a point around the origin by 270 degrees, (x,y) becomes (y,-x).
We don't really need to cover a rotation of 360 degrees since this will bring us right back to our starting point. This means that the (x,y) coordinates will be completely unchanged!
Note that all of the above rotations were counterclockwise.
If we wanted to rotate our points clockwise instead, we simply need to change the negative values. For example, a clockwise rotation of 90 degrees is (y, -x), while a counterclockwise rotation of 90 degrees is (-y,x). This also means that a 270-degree clockwise rotation is equivalent to a counterclockwise rotation of 90 degrees.
Topics related to the Rotations
Flashcards covering the Rotations
Common Core: High School - Geometry Flashcards
Practice tests covering the Rotations
Common Core: High School - Geometry Diagnostic Tests
Advanced Geometry Diagnostic Tests
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