1. The problem statement, all variables and given/known data Let A and B be elements of the line EF such that A=/B prove that the line AB=EF 2. Relevant equations Axiom that two points determine a unique line and that the intersection of two lines has two distinct points then these lines are the same. 3. The attempt at a solution If A and B are two distinct points they then determine a unique line say X. Let EF=Y then the intersection of X and Y contains at least two distinct points therefore X=Y so AB=EF. Is that sufficient?