梯形面积 by Edward Knote

GeoGebra 命令及参数

1. Segment(A, B) → a
2. Line(C, a) → b
3. Point(b) → D
4. Polygon(A, C, D, B) → P, a_1, b_2, d, b_1
5. Midpoint(D, B) → E
6. Rotate(A, -α, E) → A'
7. Rotate(C, -α, E) → C'
8. Rotate(D, -α, E) → D'
9. Rotate(B, -α, E) → B'
10. Polygon(A', C', D', B') → P', a', c', d', b'
11. Line(A, B) → e
12. OrthogonalLine(C, e) → f
13. Intersect(f, e) → F
14. Segment(C, F) → h
15. Segment(A, F) → c
16. Midpoint(B', A') → G
17. Midpoint(D', C') → H
18. If(α ≥ 0°, H) → I
19. If(α > 0°, H) → J
20. If(α > 0°, G) → K