"Three lines and octagons" is the basic knowledge of junior high school mathematics. It refers to the eight angles formed by the intersection of two straight lines with one straight line in the same plane, which is called "three-line octagon". Using geometric sketchpad to construct "three lines and eight sides" mathematics experiment can break through the difficulties of traditional teaching and achieve better teaching results.

In the courseware shown in the above figure, click the "Decompose Isometric" operation button to decompose the isometric formed by the intersection of two straight lines to the right side of the drawing board, which is convenient for students to watch. After decomposition, you can clearly see four groups of equal angles.

In this courseware, click the button of "Decompose Internal Angle", and the internal angle formed by the intersection of two straight lines and one straight line can be decomposed to the right side of the drawing board, which is convenient for students to watch. After decomposition, two groups of internal angles can be clearly seen.

In this courseware, click the operation button "Decomposition of ipsilateral internal angle" to decompose the ipsilateral internal angle formed by the intersection of two straight lines to the right side of the drawing board, which is convenient for students to watch. After decomposition, we can clearly see two groups of internal angles on the same side.