According to the given statement, the length AD is the absolute value of the difference of the coordinates of A and D. Let's interpret this statement algebraically so that we can more easily think about which postulate is being used.
Phrase
Algebraic interpretation
AD is
AD =
the absolute value of
| |
the difference of the coordinates of A and D.
A-D
We can combine these pieces to make an equation.
AD = |A-D|
This is an example of the Ruler Postulate which, when applied to our case, states the following.
The distance between points A and D, written as AD, is the absolute value of the difference of the coordinates of A and D.
