http://tube.geogebra.org/material/show/id/177015 (Download GeoGebra File)
Drag the red point to make the two lines parallel.
What is the relation of the slopes of parallel lines? 拖拉紅點，令兩綫平行。
平行綫的斜率有甚麼關係？ |
Key Stage 3 (Junior Secondary) > 3.2 Measures, Shape & Space 度量、圖形與空間 > Coordinates Geometry of Straight Lines 直線的坐標幾何 >