again, sorry, never used this site before. The actual question is this: Answer the following questions for Proof 2: (a) What is the length of segment MN? (b) What is the length of segment BC? (c) What is the length of segment AD? (d) What is the sum of the lengths of segments AD and BC?

The points A, B, C are in one line, and M, N are midpoints of segments AB, AC. BC=2MN when the points A,B,C are in the order B,C,A and M,N are midpoints of segments AB and AC and A must be also midpoint of segment BC.If points are in order b,a,c equidistant from each other than M is midpoint of AB and N is midpoint of AC so BA=2M=MN and AC=2N=MN so as we have BC=BA+AC so BC=MN+MN=2MN.