Question

AB and BC share point B to form AC. If AC=7 and BC=5, then what is the length of AB?

Answer 1

$|AC|=7;\ |BC|=5\\\\|AC|=|AB|+|BC|\\\\|AB|+5=7\ \ \ \ \ |subtract\ 5\ from\ both\ sides\\\\\boxed{|AB|=2}$

Answer 2

A                    B                     C
The whole segment is AC,AC=7,BC=5.
                                    AB=?
                                    AC-BC=AB
                                    7-5=2