 So tonight's videos are on section 10.3. This first video we're just going to review what we talked about yesterday with arc length and arc measure. So remember from yesterday that arc measure represents the same angle as the central angle of the arc. So when we are asked to find the measure of arc AB, here's arc AB and that measure has to be equal to its central angle, which is this angle of 100 degrees. So the first thing we're going to write in here is 100 degrees. Now by the way, on your note sheet you need to copy this picture down. Do arc AB so that there's a 100 degree angle here and you can see that the radius is 5 inches. Okay so let's move to arc length. Now remember that arc length is actually the distance if you were to start at A and walk around the circle so that you end up at point B, that is the arc length. So in order to find that we use the formula, remember the measure of arc AB over 360 degrees times the circumference of the circle. So we've already got the measure of arc AB is 100, so 100 over 360. And now we need to find the circumference of our circle. So remember that circumference is equal to pi times diameter and if the radius of this circle is 5, the diameter of this circle would be 10. And so the circumference of this circle is 10 pi. So I'm going to enter that here, 10 pi over 1 and now I'm going to do some reducing. So 100 over 360, the zeros cancel if you divide both by 10, so we have 10 over 36 and if we think about what goes into both 10 and 36, we come up with 2 goes into 10 5 times and 2 goes into 36 18 times and we're going to multiply that by 10 pi. And so we end up with 50 pi over 18. So 50 pi over 18, we can actually reduce a little bit further. So we know that 2 also goes into both 50 and 18, so we're going to reduce this to 25 pi over 9. So we would say that this has an arc length of 25 pi over 9.