梯形面积 - 平行四边形版本

GeoGebra 命令及参数

1. Line(A, B) → a_2
2. Line(C, a_2) → b_5
3. Point(b_5) → D
4. Segment(A, B) → b_2
5. Segment(B, D) → d
6. Segment(D, C) → b_1
7. Segment(C, A) → f
8. Midpoint(d) → E
9. Polygon(A, B, D, C) → poly1, a_1, b_3, d_1, c_1
10. Rotate(A, Slide°, E) → A'
11. Rotate(B, Slide°, E) → B'
12. Rotate(D, Slide°, E) → D'
13. Rotate(C, Slide°, E) → C'
14. Polygon(A', B', D', C') → poly1', a', b', d', c'
15. OrthogonalLine(A, b_1) → g
16. Intersect(g, b_1) → F
17. Segment(A, F) → h
18. Angle(D, F, A) → α