 So we've now covered most of the theorems in part one and part two. All we have left to look at is intersecting chords. What do you notice about the relationship between the lengths of each segment of chord? This is known as the intersecting chord theorem. When two chords intersect each other inside a circle, the product of their lengths are equal. So four multiplied by nine is equal to three multiplied by twelve, both equal thirty-six. So just remember that intersecting chord theorem means a multiplied by b equals c multiplied by d. But what happens when the lines intersect outside of the circle? Chords are inside a circle. A line passing through a circle at two points is actually called a second. Notice that the eight and the six are the whole lengths of the seconds. So from a to c and from a to e. A to c is ten and a to e is eight. So we looked at the intersecting chord theorem before and now we're looking at the intersecting second theorem. If you multiply the length of a b to the length of a c, it will equal the same thing as the length of a d multiplied by the length of a e. So just be careful to really make sure that you're multiplying by the whole length of a to e and not accidentally just multiplying by d e. So here's the test. Can you remember all nine theorems? Pause the video, jot them down, making sure you use the correct terminology and click play when you're ready to check. How did you get on? So that is all there is for circle theorems. As well as the nine theorems that we've just looked at, you will also come across parallel line angles and isosceles triangles quite a lot to keep these in mind.