 Section 10.5 is all about tangents and just a quick video on some vocabulary. A tangent is a line that intersects the circle at exactly one point. And that's important. There's one point where it intersects the circle is called the point of tangency. And that point of tangency will always make a right angle with a radius or a diameter of a circle. And so anytime you are told that you have a tangent line, you can always draw in the right angle symbol and you know that both sides there are going to equal 90 degrees. The radius or the diameter with a tangent will be perpendicular.