Students will learn how to identify the radius and the coordinates for the center of a circle given an equation. They will also learn how to find the equation of a line which is tangent to a circle at a given point. They will also learn how to find the length of a line segment which is tangent to a circle, and where one endpoint lies on the circle. Here is one example problem for each of the four aforementioned skills. Students will also learn the equation of a semicircle, as demonstrated here.