How does a geometric artboard make a tangent of a circle outside a circle?

The specific steps are as follows:

1. Draw a Circle

Open the geometry artboard. Click the side bar Circle tool to draw a circle O, and then use the DOT tool to find a point on the circle, as shown in the following figure.

Draw a circle O with the Circle tool and take a point a

2. Make the Tangent

Click the sidebar "Custom Tool"--the Circle tool--makes a circle tangent outside the circle.

To make a circle tangent to a point outside the circle below the custom tool

Click the Center o with the mouse, then click a point above the circle with the mouse, then the tangent appears, you can move the mouse to determine the point outside the circle.

Click the Center o and point A over the circle to make the tangent of the circle with the mouse