Lesson 8.1 · Geometry
Attributes of shapes
Shapes are everywhere: a slice of pizza, a door, a clock. To name a shape, you look at its sides and corners. Its color and size don't change its name.
Sides and corners
A side is a straight line that makes up the edge of a shape. A corner is where two sides meet.
Count the sides of this triangle: 1, 2, 3. Count the corners: 1, 2, 3.
Shapes to know
| shape | sides | corners |
|---|---|---|
| triangle | 3 | 3 |
| square | 4, all the same length | 4 square corners |
| rectangle | 4 | 4 square corners |
| hexagon | 6 | 6 |
| circle | 0 | 0 |
A circle is round. It has no straight sides and no corners.
A square is a special rectangle. All 4 of its sides are the same length.
What makes a shape
Sides and corners tell you the shape's name. Color, size and which way it is turned do not.
A tiny blue triangle and a big red triangle are both triangles.
Every one of these shapes is closed. The sides meet up with no gaps.
Worked example: Name the shape
A shape has 3 straight sides and 3 corners. What is it?
Three sides and three corners make a triangle.
Worked example: Turned on its side
Sam turns a triangle upside down. Is it still a triangle?
Yes! It still has 3 sides and 3 corners. Turning a shape does not change its name.
Worked example: Is it a triangle?
A shape has 3 straight sides, but there is a gap between two of them. Is it a triangle?
No. The sides must meet with no gap. The shape must be closed to be a triangle.
Common mistake
Don't name a shape by its color or size. A green shape is not a "green shape" in math. Count its sides and corners to find its name.
Practice
How many sides does a square have?
Type a number.
How many corners does a circle have?
Type a number.
Which shape has 3 sides and 3 corners?
How many sides does a hexagon have?
Type a number.
Mia has a big red square. Kai has a small yellow square. What is the same about them?
Which is not a reason a shape is a rectangle?
Leo draws one triangle and one square. How many corners are there in all?
Type a number.