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Pentagon Angle Theorems via Transformational Geometry by Mrs. Cole

Pentagon Angle Theorems via Transformational Geometry by Mrs. Cole
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2019-01-02 11:45
PolygonAngleTransformationGeometric ConstructionSlider Animation
In collections Interior and Exterior Angles of Polygons
This GeoGebra applet uses transformational geometry tools to help students discover the sum of interior and exterior angles of a pentagon. It demonstrates that the sum of interior angles is (n-2)×180° = 540° for a pentagon, and the sum of exterior angles is always 360°. The construction employs commands such as Segment, Midpoint, Ray, Circle, Intersect, CircleSector, Vector, Translate, Mirror, Dilate, Rotate, Line, If, Point, Polygon, and CircleArc. By translating, rotating, or reflecting angles, the applet visually collects all interior or exterior angles at a common vertex or along a line, making the angle-sum relationships evident. This is ideal for middle school or high school geometry classes, supporting inquiry-based learning and reinforcing concepts of angle sums, transformations, and geometric proof.

GeoGebra Commands & Parameters

  1. Segment(D, E) → i_3
  2. Midpoint(i_3) → M_3
  3. Ray(A, B) → a
  4. Ray(B, C) → b
  5. Ray(C, D) → c
  6. Ray(D, E) → d
  7. Ray(E, A) → e
  8. Circle(A, 1.5) → f
  9. Circle(B, 1.5) → g
  10. Circle(C, 1.5) → h
  11. Circle(D, 1.5) → k
  12. Circle(E, 1.5) → p
  13. Segment(C, A) → i
  14. Segment(C, E) → j
  15. Intersect(f, a, 1) → F
  16. Intersect(f, i, 1) → G
  17. Intersect(f, e, 1) → H
  18. Intersect(f, e, 2) → I
  19. Intersect(p, e) → J,
  20. Intersect(p, j) → K,
  21. Intersect(p, d, 1) → L
  22. Intersect(p, d, 2) → M
  23. Intersect(k, d, 1) → N
  24. Intersect(k, c, 2) → O
  25. Intersect(h, c, 1) → P
  26. Intersect(h, j, 1) → Q
  27. Intersect(h, i, 1) → R
  28. Intersect(h, b, 1) → S
  29. Intersect(g, a, 2) → T
  30. Intersect(g, b, 1) → U
  31. Intersect(g, a, 1) → V
  32. CircleSector(A, F, G) → q
  33. CircleSector(A, G, H) → r
  34. CircleSector(B, U, V) → s
  35. CircleSector(C, P, Q) → t
  36. CircleSector(C, Q, R) → c_1
  37. CircleSector(C, R, S) → d_1
  38. Intersect(k, c, 1) → W
  39. CircleSector(D, O, N) → e_1
  40. CircleSector(D, N, W) → f_1
  41. CircleSector(E, M, J) → g_1
  42. CircleSector(E, J, K) → h_1
  43. CircleSector(E, K, L) → k_1
  44. CircleSector(A, I, F) → p_1
  45. CircleSector(B, T, U) → q_1
  46. Intersect(h, b, 2) → Z
  47. CircleSector(C, Z, P) → r_1
  48. Vector(A, B) → u
  49. Vector(C, B) → v
  50. Vector(E, D) → w
  51. Vector(C, D) → u_1
  52. Vector(C, E) → v_1
  53. Vector(A, E) → w_1
  54. Translate(d_1, v) → s_1
  55. Mirror(s_1, B) → t_1
  56. Dilate(A, If[0 < l ≤ 1, 1 - l, 0], B) → A'
  57. Dilate(C, If[0 < l ≤ 1, 1 - l, 0], B) → C'
  58. Dilate(A, If[1 < l ≤ 2, 2 - l, 0], E) → A'_1
  59. Dilate(C, If[1 < l ≤ 2, 2 - l, 0], E) → C'_1
  60. Dilate(C, If[2 < l ≤ 3, 3 - l, 0], D) → C'_2
  61. Vector(A, B) → a_1
  62. Vector(C, C') → b_1
  63. Vector(A, A'_1) → i_1
  64. Rotate(E, If[2 < l ≤ 3, (((-(l - 2)) * 180))°, -180°], M_3) → E'
  65. Vector(E, E') → j_1
  66. Vector(C, C'_2) → l_1
  67. Vector(C, C'_1) → m_1
  68. Translate(d_1, b_1) → c_2
  69. Translate(r, i_1) → r'_1
  70. Translate(r, w_1) → r'_2
  71. Translate(k_1, w) → d_2
  72. Translate(k_1, j_1) → e_2
  73. Translate(c_1, v_1) → f_2
  74. Translate(c_1, m_1) → g_2
  75. Translate(t, u_1) → t'
  76. Translate(t, l_1) → t'_1
  77. Translate(q, a_1) → r'
  78. Translate(d_1, b_1) → h_2
  79. Vector(A, A') → n_1
  80. Line(E, C) → a_2
  81. Line(E, D) → b_2
  82. Segment(E, C) → i_2
  83. Vector(D, C) → u_2
  84. Vector(E, C) → v_2
  85. Vector(A, C) → w_2
  86. Vector(B, C) → l_2
  87. Dilate(B, If[0 < o < 1, 1 - o, 0], C) → B'
  88. Dilate(A, If[1 < o < 2, 2 - o, 0], C) → A'_2
  89. Dilate(E, If[2 < o < 3, 3 - o, 0], C) → E'_1
  90. Dilate(D, If[3 < o < 4, 4 - o, 0], C) → D'
  91. Vector(B, B') → m_2
  92. Vector(A, A'_2) → n_2
  93. Vector(E, E'_1) → s_2
  94. Vector(D, D') → t_2
  95. Translate(q_1, m_2) → c_3
  96. Translate(q_1, l_2) → d_3
  97. Translate(p_1, w_2) → e_3
  98. Translate(g_1, v_2) → f_3
  99. Translate(e_1, u_2) → g_3
  100. If(1 < o < 2, Translate[p_1, n_2]) → h_3
  101. If(2 < o < 3, Translate[g_1, s_2]) → k_3
  102. If(3 < o < 4, Translate[e_1, t_2]) → p_3
  103. Point(a_2) → A_1
  104. Point(a_2) → B_1
  105. Ray(C, B_1) → a_3
  106. Ray(E, A_1) → b_3
  107. Polygon(A, B, C, D, E) → poly1, a_4, b_4, c_4, d_4, e_4
  108. Polygon(A, B, C) → poly2, c_5, a_5, b_5
  109. Polygon(A, C, E) → poly3, e_5, a_6, c_6
  110. Polygon(E, C, D) → poly4, d_5, e_6, c_7
  111. Segment(E, A) → j_3
  112. Segment(A, B) → l_3
  113. Segment(B, C) → m_3
  114. Segment(C, D) → n_3
  115. Midpoint(j_3) → M_4
  116. Midpoint(l_3) → M_5
  117. Midpoint(m_3) → M_1
  118. Midpoint(n_3) → M_2
  119. Rotate(d_1, If[0 < l ≤ 1, (((-l) * 180))°, -180°], M_1) → k_2
  120. Rotate(C, If[0 < l ≤ 1, (((-l) * 180))°, -180°], M_1) → C'_3
  121. Segment(M_1, C'_3) → q_3
  122. Rotate(q, If[0 < l ≤ 1, ((l * 180))°, 180°], M_5) → q'
  123. Rotate(A, If[0 < l ≤ 1, ((l * 180))°, 180°], M_5) → A'_3
  124. Rotate(R, 180°, M_1) → R'
  125. Line(B, R') → s_3
  126. Segment(M_5, A'_3) → r_3
  127. Rotate(r, If[1 < l ≤ 2, (((-(l - 1)) * 180))°, -180°], M_4) → r'_3
  128. Rotate(A, If[1 < l ≤ 2, (((-(l - 1)) * 180))°, -180°], M_4) → A'_4
  129. Segment(M_4, A'_4) → p_2
  130. Rotate(t, If[2 < l ≤ 3, (((l - 2) * 180))°, 180°], M_2) → t'_2
  131. Rotate(C, If[2 < l ≤ 3, (((l - 2) * 180))°, 180°], M_2) → C'_4
  132. Segment(M_2, C'_4) → q_2
  133. Vector(E, D) → j_2
  134. Translate(L, j_2) → L'
  135. Ray(D, L') → r_2
  136. CircleArc(C, R, S) → t_3
  137. CircleArc(C, Q, R) → f_4
  138. CircleArc(C, P, Q) → g_4
  139. CircleArc(A, F, G) → h_4
  140. CircleArc(A, G, H) → k_4
  141. CircleArc(E, K, L) → p_4
  142. Segment(M_3, E') → i_4

AI Drawing Prompt Reference

Draw a pentagon ABCDE and use transformational geometry tools to demonstrate the properties of its interior and exterior angles. Start by drawing the sides of the pentagon, then draw circles centered at each vertex. Find the positions of the interior and exterior angles using intersection points, and finally use transformations like translation, rotation, and reflection to gather all interior or exterior angles at a common vertex or along a line, visually showing that the sum of interior angles is 540 degrees and the sum of exterior angles is 360 degrees.
The prompt above was compiled from the original drawing commands and is for reference only.