Grade 3 (age 8-9)

grade 3 Plane Figures

Look around and you will find shapes everywhere: a triangle on a yield sign, a rectangle on the board, a circle on the clock. For shapes made of straight sides, counting the vertices and sides tells you whether a shape is a triangle or a quadrilateral. A rectangle has four right angles, a square is a rectangle whose four sides are also equal, and a circle has no sides or vertices, because every point on it is the same distance from the center. Switch shapes with the buttons and change the size; however big the shape gets, the number of vertices and sides stays the same.

What Is a Shape?

📐 Shapes Around Us

①A whiteboard and a book cover are rectangles

②A wall clock and a plate are circles

③A yield sign is a triangle

④When you look at a shape, first check whether it is closed in by straight sides or curves all the way around

Looking Closely at Shapes

Shape size10

💡 Parts of a Shape

①A side is one of the straight lines that close in a shape

②A vertex is a point where two sides meet

③Two sides that meet at a vertex form an angle; the square corner you get by folding a sheet of paper neatly twice is a right angle

④A circle has no vertices or sides; it has a center, and a radius is a line from the center to the circle

⑤A square also has four right angles, so a square is a rectangle too

Summary

Triangle

3 vertices, 3 sides, 3 angles

A shape closed in by 3 straight sides

Quadrilateral

4 vertices, 4 sides, 4 angles

A shape closed in by 4 straight sides

Circle

All points the same distance (the radius) from the center

Every radius of a circle has the same length

🎯 Summary

①A triangle has 3 sides and 3 vertices, and a quadrilateral has 4 of each

②A rectangle has four right angles, and its opposite sides are equal

③A square has four right angles and four equal sides

④Every square is a rectangle, but not every rectangle is a square

⑤A circle has no sides or vertices, and all its radii are the same length

Examples and Unit Test

Example 1

What is the name of a shape with 3 sides, 3 vertices and 3 angles?

A shape with straight sides is named by its number of sides.

It has 3 sides, so it is a triangle.

▸ Triangle

In a shape with straight sides, the numbers of sides, vertices and angles are all the same.

Example 2

What do we call a quadrilateral whose four sides are all equal and whose four angles are all right angles?

A quadrilateral with four right angles is a rectangle.

A rectangle whose four sides are also all equal is a square.

▸ Square

A square is a special rectangle whose four sides are all the same length.

Unit Test

Which shape has no vertices or sides and is made of points that are all the same distance from the center?

①triangle

②rectangle

③circle

④square

▸ ③ circle

Triangles, rectangles and squares all have sides and vertices.

The shape with no sides or vertices, made of points the same distance from the center, is a circle.

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Equal Sharing

Introduction to Circles

Last updated 2026-10-17