Look around your classroom. The door is a rectangle, the clock is a circle, the pizza slice is a triangle, and the tile on the floor may be a square. Shapes are everywhere! In this chapter we learn to name, describe, and draw common 2-D shapes.
What will we learn?
We will identify and name basic flat (2-D) shapes: circle, triangle, square, and rectangle. We will also count their sides and corners (vertices).
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Key Concepts
Circle: A round shape with no straight sides and no corners.
Triangle: A shape with 3 straight sides and 3 corners.
Square: A shape with 4 equal sides and 4 corners. All angles are equal.
Rectangle: A shape with 4 sides and 4 corners. Opposite sides are equal. A square is a special rectangle.
Side: A straight line that forms part of a shape.
Corner (vertex): The point where two sides of a shape meet.
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Worked Examples
How many sides does a triangle have?
A triangle has 3 sides and 3 corners.
Name a shape that has 4 equal sides and 4 corners.
A square has 4 equal sides and 4 corners.
Priya drew a shape with 4 sides where opposite sides are equal but not all 4 sides are equal. What shape is it?
It is a rectangle.
Look at a coin. What shape is it?
A coin is round — it is a circle.
A door has 4 sides. The longer sides are equal and the shorter sides are equal. What shape is the door?
The door is a rectangle.
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Common mistakes
- A square is also a rectangle (all squares are rectangles, but not all rectangles are squares).
- A circle has NO sides and NO corners — students sometimes say it has 1 side.
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Summary
Flat shapes around us include circle, triangle, square, and rectangle. We can tell them apart by counting sides and corners. Shapes help us describe the world around us.