A triangle is a 2D shape with three sides and three angles. The angles in a triangle add up to 180°. The properties of different kinds of triangles are listed below.

The area of the rectangle is 8 cm 2. Two triangles make the rectangle. The area of one triangle is half the area of the rectangle.

The shape of a structure affects how strong it is. Rectangles, arches, and triangles are the most common shapes used to build big structures. What happens when you push the side of a rectangle?