 So let's discover some more circle theorem, so that we can solve all types of geometrical problems. We discovered these four theorems in part one, so if you aren't familiar with some of these, watch that video first. Before we start, you should know what all of these key terms mean. If you aren't sure, watch that video first. So let's go discovering some more theorem. What do you notice about the angle between the tangent and the radius? Remember that a tangent is the line that touches a circle at only one point. That's theorem five. The angle between a tangent and a radius is 90 degrees. What do you notice about the length of the tangent? The lengths of two tangents from a point to a circle are equal. This is useful to bear in mind as it means you have two identical triangles. So we've got tangent and radius given 90 degrees and we've got two tangents of the same length. There's just one final thing to learn about tangent and circles. Can you see what's happening with the angles? Theorem is known as the alternate segment theorem. The angle between a tangent and a chord is equal to the angle in the alternate segment. I've always just thought of it as the angle that's furthest away, so it can't be this angle because it's next to it and it can't be this angle because it's on the same line. So that means it has to be this angle, the alternate segment theorem. So this one can be tricky to remember. Maybe you want to write it down somewhere that you'll see it a lot, like on the back of your bedroom door. So you've now covered nearly all of the theorems. All we have left to look at is the final two theorems to do with chords, which we'll see in part three. Can you remember all three theorems that we've looked at in this video? Pause the video, jot them down, making sure you use the correct terminology, and click play when you're ready to check. How'd you get on? So here are three questions for you to do. Question three requires you to use your knowledge of parallel line angles and esosceles triangles. Pause the video, find the missing angles, and click play when you're ready to check. How did you do? So there we have seven circle theorems. When you're on your way home from school or waiting in a queue, see how many you can remember. In part three, we're going to discover the final two theorems that are to do with intercepting chords.