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Similarity

2. Measure the lengths of sides and angles of both shapes, then find the ratio of the
corresponding side lengths.
3. Use your observations to make a general conclusion about the shapes, and explore
additional sources such as the internet and books to enrich your competence.

4. Reflect on real objects around you with similar features and characteristics and
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share your insights.
Mathematics for Secondary Schools Similar figures are geometric shapes that have the same shape but differ in size. They

maintain the same ratio of corresponding sides and angles. Study Figure 3.1 which
illustrates the concept of similar objects.

Figure 3�1: Pictures of similar blackboards

In Figure 3.1, the objects are similar because they have the same shape but differ in size.
Based on this experience, a simple method of obtaining similar figures is by uniformly
scaling (enlarging or shrinking) the original figure. Engage in Activity 3.2 to explore
more about similarity of figures.

Activity 3�2: Using computer applications to demonstrate similarity of figures
1. Use a software of your choice (MS Word, Desmos, GeoGebra) to create various
shapes.

2. Copy and paste the shapes into a new workspace, then resize by enlarging or
reducing the figures.
3. Observe the changes in size in terms of sides and angles and discuss your
findings based on the similarity of figures.

Similar triangles
Triangles are similar when their corresponding angles are equal and their corresponding

sides are proportional. Consider the pair of triangles shown in Figure 3.2.

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Student's Book Form Two

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