### Video Transcript

Which of the following is another name for the straight line 𝐴𝐵? The choices are chord, radius, diameter, and tangent.

Well, let’s have a look at each of these in turn. So we’re gonna start with the chord. Well, first of all, the chord is a line that joins two parts of our circumference, but doesn’t go through the centre of the circle. And it also forms a segment which is shown by the shaded-in area here. So therefore, this is not the name for the straight line 𝐴𝐵.

Next, we have the radius. Well, the radius is a straight line from the centre of our circle out to the edge or the circumference of the circle. So yet again, this is not the straight line 𝐴𝐵. So this is not the correct answer.

So next, we have the diameter. And the diameter is again a straight line. But this is a straight line that joins two points that are on the circumference of the circle. However, the difference between this and the chord is that the diameter must go through the centre of the circle. And also, we have a little relationship. And that is that the diameter is equal to two multiplied by the radius or twice the length of the radius. And that’s because the radius goes from the centre to the edge, whereas the diameter goes from the edge to the centre to the edge. So therefore, again, this is not the straight line 𝐴𝐵.

So then, finally, we have a tangent. And the tangent is a straight line again. But this time, it’s a straight line that touches the circle at only one point. Now, it’s also worth noting that at this point the tangent is perpendicular or at right angles to the radius at this point, so if we took the radius from this point to the centre of the circle. So therefore, the other name for the straight line 𝐴𝐵 is the tangent of the circle.