４つの弧に囲まれた部分の面積 ver.2

Topic:Angles, Area, Circle, Congruence, Cosine, Equilateral Triangles, Geometry, Mathematics, Plane Figures or Shapes, Pythagoras or Pythagorean Theorem, Quadrilaterals, Right Triangles, Sine, Square, Symmetry, Geometric Transformations, Triangles, Trigonometric Functions