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Grade 3 (age 8-9)

grade 3 Plane Figures

Plane Figures

Look around and you will spot shapes everywhere, like triangular signs, rectangular blackboards, and round clocks. Every figure has vertices, sides, and angles, and counting them shows whether it is a triangle or a quadrilateral. A square has four equal sides, a rectangle has equal opposite sides, and a circle has no sides or vertices at all. Switch shapes with the buttons and change the size. Growing bigger does not change how many sides or vertices there are.

What is a Shape?

📐 Shapes Around Us
①The classroom blackboard is a rectangle
②A clock is a circle
③Triangles in road signs
④Shapes are made of points, lines, and faces

Let's Look at Shapes

10
💡 Parts of a Shape
①Vertex: where sides meet
②Side: line connecting vertices
③Angle: gap between two meeting sides
④Circle has no vertices/sides — has center and radius
⑤A square has four equal sides and four right angles, so it is a rectangle too

Summary

Triangle
3 vertices + 3 sides + 3 angles
Surrounded by 3 straight lines
Quadrilateral
4 vertices + 4 sides + 4 angles
Surrounded by 4 straight lines
Circle
Set of points at equal distance (radius) from center
Round shape with no vertices or sides
🎯 Key Points
①Triangle: 3 sides, 3 vertices
②Quad: 4 sides, 4 vertices
③Square has 4 equal sides and right angles
④Rectangle has equal opposite sides and right angles. A square is a rectangle too
⑤Circle has no sides/vertices, equal distance from center

Examples and Unit Test

Example 1
What is the name of a shape with 3 sides, 3 vertices, and 3 angles?
1
Tell shapes apart by their number of sides, vertices, and angles.
2
A shape with 3 sides, 3 vertices, and 3 angles is a triangle.
▸ Triangle
In one shape, the number of sides, vertices, and angles are all equal.
Example 2
What is the name of a quadrilateral with 4 equal sides and 4 right angles?
1
A quadrilateral has 4 sides and 4 vertices.
2
The one with all 4 sides equal and all 4 angles right is a square.
▸ Square
A square is a rectangle because all four angles are right. It is the special rectangle whose four sides are also equal.
Unit Test
Which shape has no vertices or sides and is at equal distance from a center?
①triangle
②rectangle
③circle
④square
▸ ③ circle
1
A circle has no straight sides and no vertices.
2
A circle is the set of points at equal distance (radius) from a center.
← Previous
Equal Sharing
Next →
Introduction to Circles