5. Perpendicular lines

When two lines intersect each other at right angles, they are perpendicular to each other.

 

 

Here, $\overline{AB}$ and $\overline{CD}$ meet at right angles to each other. Therefore, $\overline{AB}$ and $\overline{CD}$ are perpendicular to each other.

 

When a perpendicular line divides another line into two halves, then it is called a perpendicular bisector.

 

 

We know that $\overline{AB}$ is perpendicular to $\overline{CD}$. Also, $AO = OB$.

 

Thus, $\overline{CD}$ divides $\overline{AB}$ into two halves.

 

Therefore, $\overline{CD}$ is the perpendicular bisector of $\overline{AB}$.