圆的方程（V3）：开放中间问题

GeoGebra 命令及参数

1. Sequence(i, i, -9, 9, 1) → hlist
2. Sequence(i, i, 0, 9, 1) → tenslist
3. Sequence(i, i, -9, 9, 1) → klist
4. Sequence(i, i, -9, 9, 1) → xlist
5. Sequence(i, i, -9, 9, 1) → ylist
6. SelectedElement(hlist) → H
7. SelectedElement(klist) → K
8. SelectedElement(xlist) → xc
9. SelectedElement(ylist) → yc
10. SelectedElement(tenslist) → tensdigit
11. Sequence(i, i, 1, 9, 1) → oneslist
12. SelectedElement(oneslist) → onesdigit
13. Center(eq1) → B
14. Point(eq1) → C
15. Segment(B, C) → f
16. Midpoint(f) → D
17. Length(Mode[l1]) → b
18. If(b ≟ 0, "√", "×") → text5
19. Polygon(B, E, A) → t1, a_1, b_1, e
20. Segment(A, B) → g
21. Segment(B, E) → h
22. Segment(A, E) → i
23. Angle(A, E, B) → α
24. Midpoint(C, B) → F