Chapter 5 - Relationships Within Triangles - 5-5 Indirect Proof - Practice and Problem-Solving Exercises - Page 321: 19

If $X$ is a point on the perpendicular bisector of $\overline{AB}$, then $\overline{XB}$ is not congruent to $\overline{XA}$.

For the first step in an indirect proof, we have to negate the "then" part of the statement. So we can write that if $X$ is a point on the perpendicular bisector of $\overline{AB}$, then $\overline{XB}$ is not congruent to $\overline{XA}$.