康威圆与勒洛三角形:过六点的等宽曲线
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① 本范例演示了康威圆(Conway circle)与勒洛三角形(Reuleaux triangle)的关联:康威圆经过三角形三边延长线上的六个特定点,而一个广义的勒洛三角形(等宽曲线)也恰好经过这六个点。② 核心数学概念包括:三角形内切圆、外接圆、等宽曲线、几何构造、旋转与对称。③ 作图要点:使用GeoGebra命令如Polygon(多边形)、Circle(圆)、Line(直线)、Intersect(交点)、Segment(线段)、CircleArc(圆弧)、Rotate(旋转)、Center(中心)、OrthogonalLine(垂线)等,构造了三角形ABC、内切圆c、以及通过旋转和圆弧生成的勒洛三角形,涉及对象包括anim、A、B、C、t1、c、a、b、d、e、f、g、h、i、D、E、F、G、H、I、j、k、l、m、n、p、q、r_1、s、t、c_1、d_1、e_1、f_1、g_1、r、h_1、r2、r3、a0。④ 适合高中及以上学段,用于几何构造、等宽曲线性质、以及动态数学探索,也可作为教师演示或学生自主探究的素材。
GeoGebra 命令及参数
Polygon(A, B, C) → t1, c, a, bCircle(A, a) → dCircle(B, b) → eCircle(C, c) → fLine(A, B) → gLine(A, C) → hLine(C, B) → iIntersect(d, g, 1) → DIntersect(d, h, 1) → EIntersect(f, i, 1) → FIntersect(f, h, 2) → GIntersect(e, g, 2) → HIntersect(e, i, 2) → ISegment(C, B) → jSegment(A, D) → kSegment(A, E) → lSegment(B, A) → mSegment(C, F) → nSegment(C, G) → pSegment(A, C) → qSegment(B, I) → r_1Segment(B, H) → sCircle(D, E, I) → tCircleArc(A, E, D) → c_1CircleArc(A, G, H) → d_1CircleArc(B, D, F) → e_1CircleArc(C, F, G) → f_1CircleArc(B, H, I) → g_1Min(1, Max[anim - 1, 0]) → rCircleArc(C, I, E) → h_1Min(1, Max[anim - 2.2, 0]) → r2Min(1, Max[anim - 3.4, 0]) → r3Segment(E, G) → a0Rotate(E, (r * Angle[C, A, B]), A) → E'Rotate(G, (r * Angle[C, A, B]), A) → G'Segment(E', G') → a1Rotate(E', (r2 * Angle[A, B, C]), B) → E''Rotate(G', (r2 * Angle[A, B, C]), B) → G''Segment(E'', G'') → a2Rotate(E'', (r3 * Angle[B, C, A]), C) → E'''Rotate(G'', (r3 * Angle[B, C, A]), C) → G'''Segment(E''', G''') → a3Circle(E''', a) → k_1Circle(G''', b) → p_1Intersect(k_1, a4, 1) → JIntersect(p_1, a4, 1) → KSegment(E''', J) → i_1Segment(J, K) → j_1Segment(K, G''') → l_1CircleArc(A, E, E') → aa1CircleArc(A, G, G') → aa2CircleArc(B, D, E'') → aa3CircleArc(B, H, G'') → aa4CircleArc(C, F, E''') → aa5CircleArc(C, I, G''') → aa6Center(t) → LMin(1, Max[anim + 0.2, 0]) → r0Rotate(E, (r0 * 360°), L) → E'_1OrthogonalLine(L, g) → m_1Intersect(g, m_1) → MCircle(L, M) → q_1Segment(L, E'_1) → n_1Segment(L, E) → s_1Intersect(q_1, s_1) → N,Rotate(N, (r0 * 360°), L) → N'CircleArc(L, N, N') → ptcCircleArc(L, E, E'_1) → ptc2OrthogonalLine(G''', a4) → t_1OrthogonalLine(E''', a4) → a_1