Parallel and Perpendicular Lines: Slope Conditions

This GeoGebra example demonstrates the slope criteria for parallel and perpendicular lines in the Cartesian coordinate plane, including the special fact that a horizontal line has slope zero. Core mathematical concepts include linear functions, equal slopes for parallel lines, negative reciprocal slopes for perpendicular lines, and coordinate-geometric position relationships. The construction uses GeoGebra commands Line, Slope, Intersect, Segment, and Distance, together with points A, B, O and lines a through i, while text objects such as TextFO and TextGO display computed results dynamically. It is suitable for middle school students studying linear functions and line relationships, and can also serve as an interactive demonstration or review tool in high school analytic geometry classes.