Because u might need it in the real world.
Answer: A three-sided polygon is a triangle.
There are several different types of triangle (see diagram), including: Equilateral – all the sides are equal lengths, and all the internal angles are 60°. Isosceles – has two equal sides, with the third one a different length.
Step-by-step explanation:
The answer to this problem would be 12. If you need to show work just comment.