Question

Macy is dressed as a geometric shape for Halloween. She came up with a riddle to introduce herself to her friends.
She says, "I am a plane figure with three sides, and the sum of two of my angles is 90°".

What is Macy's costume?

Answer 1

Triangles are plane figures with three sides.
The sum of two angles of the triangle is given to be 90°.

Sum of two angles + Third angle = 180°
Third angle = 90°

Thus, Macy's costume is that of a right-angled triangle.