Similar Figures, Dilations, and Scale Factor

Topic #3 Properties of Similar Figures

By William Glynn

A dilation is a transformation that ​enlarges or reduces an original figure proportionally.

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Dilations!

Enlargement = gets bigger​

Reduction = gets smaller​

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Preimage = the original figure (before)

Image = the resulting figure​ (after)

​The pre-image and image of the elephant show an enlargement.

​Preimage vs. Image

We say that the preimage and its image are similar figures.

Triangle A is dilated to get Triangle B. What is the scale factor?

Example: Finding the scale factor

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Is this an enlargement or a reduction?

Which Triangle is the preimage?

​How else could you have found the same answer?

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​*use the grid to count side lengths*

Multiple Choice

Triangle A is dilated to form Triangle B.

Is this an enlargement or a reduction?

• Enlargement (gets bigger)

• Reduction (gets smaller)

Multiple Choice

Triangle A is dilated to form Triangle B.

What is the scale factor?

• $$2$$   

• $$\frac{1}{3}$$  

• $$3$$  

Multiple Choice

Triangle FHS is dilated to form Triangle GEO.

Is this an enlargement or a reduction?

• Enlargement (gets bigger)

• Reduction (gets smaller)

Multiple Choice

Triangle FHS is dilated to form Triangle GEO.

What is the scale factor?

• $$\frac{1}{3}$$  

• $$\frac{1}{2}$$  

• $$\frac{1}{4}$$