When two non-parallel lines cross, they create an angle between them. If the lines are perpendicular, they form a 90-degree angle. Otherwise, they create an acute, obtuse or other type of angle. Every angle has a "slope." For instance, a ladder against a wall has a slope whose value varies according to the angle of the ladder. Using a little geometry, you can compute the angle between two intersecting lines by determining their slopes.

# How to Calculate Angles Between Two Lines

By Kevin Lee lines of lights image by Qdigits from Fotolia.com