A ray of light is emitted from a point on the wall of a mirror-covered semicircle and reflects four times as shown to return to the same spot. If the radius is 1, what is the length of the path?
A unit square paper is folded as shown. What is the red area?
Two equilateral triangles and a square. What’s the angle α?
A semicircle and two tangent circles (tangency point shown). What is the angle α?
A right triangle with two angle bisectors. What is red : blue?
A regular hexagon of which the centre is a vertex of an equilateral triangle. What is the angle α?
Two equilateral triangles on a blue line segment. Prove that the red line segment is parallel to it.
Several triangles and three congruent angles. Prove that the red point is the incentre of the yellow triangle.
A square containing an isosceles triangle. What’s the angle α?
Two squares and two equilateral triangles. Prove that the red vertices also form an equilateral triangle.