Question

Which statement describes the order of rotational symmetry for an isosceles triangle?

An isosceles triangle has an order 0 rotational symmetry because there is no angle at which it can be rotated onto itself.
An isosceles triangle has an order 1 rotational symmetry because it does not have all congruent angles.
An isosceles triangle has an order 2 rotational symmetry because it has 1 pair of congruent angles.
An isosceles triangle has an order 3 rotational symmetry because it has 3 angles.

Answer 1

The correct choice is the second: "An isosceles triangle has an order 1 rotational symmetry..."

Explanation: A non‑equilateral isosceles triangle only maps onto itself under the full 360° rotation (the identity), so it has rotational symmetry of order 1. (An equilateral triangle, by contrast, has order 3.)