On segment AB, point C lies between A and B with AC = CB. A student claims AC = 1/2 AB. Which axiom best supports the step that 'AC + CB = AB'?

Question

Accepted Answer

The whole is equal to the sum of its parts. AB is split into the two parts AC and CB, so AB = AC + CB. With AC = CB this gives AC = 1/2AB.

On segment AB, point C lies between A and B with AC = CB.
A student claims AC = $\frac{1}{2}$ AB.
Which axiom best supports the step that 'AC + CB = AB'?