What is Square, rectangle, triangle, circle? — Mathematics

Definition 5.1 Primary & Middle School Mathematics · Chapter 5 — Shapes and Space

the triangle has $3$ sides and $3$ corners;
the square has $4$ equal sides and $4$ corners;
the rectangle has $4$ sides and $4$ corners, with opposite sides equal (a stretched square);
the circle is perfectly round: no sides, no corners.

The four basic shapes. To name a shape, do not trust the first glance: count its sides and corners. — The four basic shapes. To name a shape, do not trust the first glance: *count* its sides and corners.

Examples

Example 5.2 (Tilted shapes are still shapes)

A square standing on its corner is still a square — four equal sides, four corners — even if it looks like a kite. Turning a shape does not change what it is.

Example 5.3 (Shape hunt)

In the classroom: the board is a rectangle, the clock a circle, a folded napkin can be a triangle, some windows are squares. Real objects are not perfect shapes, but their faces are close to them (solids and their faces return in Chapter 11).

Read in context →