Lesson Notes By Weeks and Term v4 - SHS 2

Lesson Video

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Performance objectives

• Define enlargement and reduction.
• Explain the properties of enlargement.
• Calculate the image of a shape given a scale factor and a center of enlargement.
• Draw an original shape and its enlargement on a graph.

Lesson summary

Today, we are exploring a type of geometric transformation called enlargement. This is something we see and use every day in Ghana without even thinking about it. When you use a photocopier to make a document bigger, you are performing an enlargement. When you zoom in on a photo on your phone to see a friend's face more clearly, you are using enlargement. Architects in Accra and Kumasi use this concept to create small-scale building plans (a reduction) that guide the construction of huge buildings. Even the beautiful Kente patterns our weavers create are often based on a small design that is scaled up.

Lesson notes

A. What is Enlargement? Enlargement is a transformation that changes the size of an object but preserves its shape. The angles of the shape remain the same, and the ratio of corresponding side lengths is constant. Object: The original shape before transformation. Image: The new shape after transformation. If the image is bigger than the object, it is called an enlargement. If the image is smaller than the object, it is called a reduction.

The two key components needed to perform an enlargement are: The Centre of Enlargement (O): This is a fixed point from which the enlargement is performed. All points on the object are 'stretched' away from or 'shrunk' towards this centre. The Scale Factor (k): This is a number that determines how much bigger or smaller the image will be compared to the object. B. The Scale Factor (k) The scale factor is the ratio of a length on the image to the corresponding length on the object.

`Scale Factor (k) = Length of a side on the image / Length of the corresponding side on the object`

It can also be defined using the distance from the centre of enlargement:

Evaluation guide

• Carry out an enlargement of a plane shape given a scale factor.
• Think -pair share activities : Learners in pairs research and make presentations on the concept of
• enlargement/reduction in transformations.
• Example : In transformation, enlargement/reduction is when the size of an object is changed without