When two lines meet and form a right angle, what term describes their relationship?

• A. Intersecting
• B. Perpendicular
• C. Similar
• D. Parallel

Answer: (B)

Perpendicular lines are two lines that meet to form a right angle. That 90-degree relationship is what defines them. Intersecting just means two lines cross, but the angle between them can be anything, so it doesn’t specify a right angle. Parallel lines never meet, so they can’t form any angle, including a right angle. Similar describes likeness in shape, not the angle between lines. If you think in slopes, a line with slope m is perpendicular to a line with slope -1/m (as long as neither is vertical), which is another handy way to recognize perpendicular relationships.