This is the eighth tutorial in the Geometer’s Sketchpad Essentials Series. In this post we are going to learn the *Rotate* command. First we are going to create a triangle and name it *ABC*, create a center of rotation point *D*, and then rotate a triangle 90 degrees.

The output of this tutorial is shown in the first figure.

1.) Using the **Point** tool, construct three points.

2.) Highlight the three points, click the **Display** menu from the menu bar, and then click the **Show Labels**.

3.) With the three points still selected, click **Triangle Interior** from the **Construct** menu.

4.) Now, use the **Point** tool to construct point *D* outside the triangle interior. After step 4, your drawing should look like the figure below.

5.) Next, we mark* D* as our center of rotation. To do this, select point *D*, click the Transform menu, and the click **Mark Center**.

6.) Now, to rotate triangle *ABC*, be sure that only the polygon and the three points are selected. Next, click the **Transform** menu, and then click **Rotate**

7.) In the* Rotate dialog box *(see Figure below), leave the value as is (90.0 degrees) and click the **Rotate** button.

8.) Display the labels of the image of the rotated triangle. The label should be *A*‘*B*‘*C*‘.

9.) Now move the points *A*, *B*, and *C*. What do you observe? What can you say about the three vertices of the rotated triangle in relation to *D*?

10.) Save your file.

Exercise: Use point A as the center of rotation and rotate the triangle by 270 degrees.