Question

what does the following notation describe?
ab ⊥ dc
two perpendicular lines
two congruent lines
two perpendicular segments

Explanation:

The notation \(\overleftrightarrow{AB}\perp\overleftrightarrow{DC}\) uses the symbol \(\perp\) which is the standard symbol for perpendicularity. The arrows above \(AB\) and \(DC\) indicate that they are lines (not just segments, as segments would have endpoints marked differently, like \(\overline{AB}\)). Congruent lines would use a different symbol (\(\cong\)) for congruence.

Answer:

two perpendicular lines