Given:

Segment AB is congruent to Segment DE
Prove:
Segment AD is congruent to BE

Note: (for the illustration)
C is the midpoint of Segment AE, B is the midpoint of Segment AC and D is the midpoint of Segment CE.

1 answer

AD = AE-DE
BE = AE-AB

AB=DE, so
AD = AE-AB = BE

You can reword that using all the "congruents" instead of = signs.