四边形内角和的几何证明与动态演示

GeoGebra 命令及参数

1. Polygon(A, B, C, D) → q1, a, b, c, d
2. Circle(A, 1.5) → e
3. Circle(B, 1.5) → f
4. Circle(C, 1.5) → g
5. Circle(D, 1.5) → h
6. Intersect(e, d, 1) → E
7. Intersect(e, a, 1) → F
8. Intersect(f, a, 1) → G
9. Intersect(f, b, 1) → H
10. Intersect(g, b, 1) → I
11. Intersect(g, c, 1) → J
12. Intersect(h, c, 1) → K
13. Intersect(h, d, 1) → L
14. CircleSector(A, F, E) → k
15. CircleSector(D, L, K) → r
16. CircleSector(C, J, I) → p
17. CircleSector(B, H, G) → q
18. Midpoint(c) → M
19. Midpoint(C, A) → O
20. Rotate(r, (-α), M) → r'
21. Midpoint(b) → P
22. Rotate(q, α, P) → q'
23. Rotate(k, α, O) → k'
24. Rotate(k', α, C) → k''