Circumcircle of Triangle
The circle that passes through all vertices (corner points) of a triangle.
Try moving the points below, and notice:
* the center (called the circumcenter) can be inside or outside of the triangle.
* the center is where three special lines cross: lines that are at right angles to the midpoint of each side of the triangle.
* also try putting the points on grid lines and see what interesting things you can discover.