Lesson Notes By Weeks and Term v5 - Grade 4

Lesson Video

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Performance objectives

• Identify and name common 2D shapes and their properties.
• Draw and classify different types of triangles.
• Identify lines of symmetry in 2D shapes.
• Create symmetrical patterns.
• Describe the properties of quadrilaterals like squares and rectangles.

Lesson summary

Geometry is all around us! From the shape of the soccer ball kicked at the stadium to the patterns on the Ndebele houses, shapes are everywhere. Understanding 2D shapes and symmetry helps us to describe, understand, and even create beautiful things. In South Africa, recognizing geometric shapes is crucial for understanding traditional art, architecture, and even everyday objects. Think of the geometric patterns in Zulu beadwork or the rectangular layout of townships. This week, we're going to explore the fascinating world of flat (2D) shapes and the magic of symmetry! We'll learn to identify different shapes, describe their properties, and discover how to find lines of symmetry.

Lesson notes

2D Shapes: 2D shapes are flat shapes that have only two dimensions: length and width. They don't have any thickness or depth. They exist on a flat plane, like a piece of paper or a chalkboard.

Let's look at some common 2D shapes: Square: A square has four equal sides and four right angles (90°). All sides are the same length.

Example:* A tile on a floor, a window pane (sometimes).

Rectangle: A rectangle has four sides and four right angles (90°). Opposite sides are equal in length. A square is a special type of rectangle.

Example:* A door, a school textbook, a soccer field.

Triangle: A triangle has three sides and three angles.

There are different types of triangles: Equilateral Triangle: All three sides are equal, and all three angles are equal (60° each).

Isosceles Triangle: Two sides are equal, and the two angles opposite those sides are equal.

Scalene Triangle: All three sides are different lengths, and all three angles are different.

Right-angled Triangle: One of the angles is a right angle (90°).

Example:* A slice of watermelon, the roof of some houses.

Circle: A circle is a round shape with no corners or straight sides. All points on the circle are the same distance from the center.

Example:* A wheel, the sun, a coin.

Quadrilaterals: These are shapes that have four sides. Squares, rectangles, parallelograms, and trapeziums are all quadrilaterals.

Parallelogram: A quadrilateral with two pairs of parallel sides. Opposite sides are equal in length, and opposite angles are equal.

Trapezium: A quadrilateral with at least one pair of parallel sides.

Symmetry: Symmetry means that a shape can be divided into two identical halves that are mirror images of each other. The line that divides the shape into two identical halves is called the line of symmetry.

Line of Symmetry: An imaginary line that divides a shape into two identical halves. If you were to fold the shape along the line of symmetry, the two halves would match up perfectly.

Examples of Symmetry: A square has four lines of symmetry: one horizontally, one vertically, and two diagonally.

A rectangle has two lines of symmetry: one horizontally and one vertically. An equilateral triangle has three lines of symmetry. An isosceles triangle has one line of symmetry. A circle has an infinite number of lines of symmetry – any line passing through the center. A scalene triangle has no lines of symmetry.

Worked example

Identifying a Shape: I see a shape with four sides. Two sides are long, and two sides are short. All the angles are right angles. What shape is it?

Solution:* It is a rectangle. Rectangles have four sides and four right angles, with opposite sides being equal in length.

Drawing a Triangle: Draw a triangle where all sides are equal in length. What kind of triangle is it?

Solution:* (Draw an equilateral triangle) It is an equilateral triangle.

Finding Lines of Symmetry: How many lines of symmetry does a square have? Draw them.

Solution:* (Draw a square and its four lines of symmetry) A square has four lines of symmetry.

Completing a Symmetrical Shape: Draw the other half of this shape to make it symmetrical (draw half a heart shape and a vertical line of symmetry).

Solution:* (Complete the heart shape so both sides are mirror images).

Guided Practice (With Solutions)

Question 1: Name the following shape and describe its properties: (Draw a circle).

Solution: The shape is a circle. It has no sides or corners. All points on the circle are the same distance from the center. It has infinite lines of symmetry passing through its centre.

Question 2: Draw a rectangle. How many lines of symmetry does it have? Draw the lines of symmetry.