Rotational symmetry means that you can spin the figure 180^(∘) or less so that it maps onto itself.
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Consider the given triangle.
This triangle has one angle that is 90^(∘) and the other two angles are acute. The sides of the triangle are notcongruent, and the triangle does not have any lines of symmetry. Therefore, rotating the triangle by any angle will not result in the triangle looking the same as it did before the rotation. Let's visualize it!
Because of this, the triangle does not have rotational symmetry because there is no rotation of 180^(∘) or less that maps the figure onto itself.
