Which of the triangles A, B, C, D, E have rotational symmetry?

Analysis:

• Triangle A: Has angles 70°, 60°, 50° (calculated as 180° - 70° - 60°). It has no rotational symmetry as all angles are different.
• Triangle B: It is an isosceles triangle with base angles 20° and 25°, which is not possible as base angles of an isosceles triangle must be equal. Assuming it is intended to be an isosceles triangle with base angles around 20° and 25°, it would have rotational symmetry of order 1 (rotational symmetry through 360°).
• Triangle C: It is an isosceles triangle with angles 31°, 31°, 118° (calculated as 180° - 31° - 31°). It has rotational symmetry of order 1.
• Triangle D: It is an equilateral triangle with all angles 60°. An equilateral triangle has rotational symmetry of order 3 (rotations by 120° and 240°).
• Triangle E: It is an equilateral triangle with all angles 60°. An equilateral triangle has rotational symmetry of order 3 (rotations by 120° and 240°).

Answer: Triangles D and E have rotational symmetry.