Varsity Tutors
Varsity Tutors: Hotmath: Practice Problems: Perpendicular and Parallel Lines
Twenty-two problems present a variety of practice working with perpendicular and parallel lines. They are given with each step to the solution cleverly revealed one at a time. You can work each step of the problem then click the "View...
University of Georgia
University of Georgia: Inter Math: Perpendicular Lines
This site from InterMath opens with a very simple definition of perpendicular lines and has links to challenging problems, more information, related terms and everyday examples of perpendicular lines.