Exercise 12 Page 525

The distance from a point to a line is defined as the shortest distance, which is trough the perpendicular segment from the point to the line. Let's consider the given diagram.

We see that the segment that measures $12$ centimeters is not perpendicular to $\overleftrightarrow{AB}.$ Conversely, the segment that is perpendicular to $\overleftrightarrow{AB}$ measures $8$ centimeters.