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Learning Objectives

  • Use similarity to generalize the results.


We know that all circles are similar to each other.

Suppose a circle has a radius of r units.

  • The scale factor of this circle (with radius r ) and the circle with radius 1 is:

r : 1, \quad \frac{r}{1}, \quad \text{or just} \quad r.

  • You know how a scale factor affects area measures:

If the scale factor is r, then the area is r^2 times as much.

Reading Check:

1. Explain how we know that all circles are similar to each other.

(Hint: Think about similar measurements that circles may have.)





2. If the scale factor of a circle is r, how does this relate to a circle’s area?





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Date Created:

Feb 23, 2012

Last Modified:

May 12, 2014
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