A line segment ad, contains points b & c such that c is between a and d, and b is between a and
c. if ab = 6, bd = 23, and ab = cd, find the length of segment bc.

If you drew out this line segment with the points in the order we are given them, the segment would be labeled as a, b, c, d in that order. We are given a measure for ab, and we are also given a measure for bd with c being ignored for a minute. The entire length of the segment can be found by adding ab and bd. 6 + 23 = ad and ad = 29. So the length of the whole segment is 29. We have the length of cd given to be equal to ab, so cd = 6. ab + bc + cd = ad and we are looking for bc. Since we have the other lengths and the length of the whole segment, we fill in accordingly: 6 + bc + 6 = 29. Solving for bc we get bc = 17.