Big Ideas Math Integrated I, 2016
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Big Ideas Math Integrated I, 2016 View details
3. Rotations
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Exercise 23 Page 567

Rotational symmetry means that you can spin the figure 180^(∘) or less so that it maps onto itself.

D and G

Practice makes perfect

Consider the given pentagon.

We want to determine the angles of rotational symmetry for the given polygon. To do so, let's draw segments from the vertices of the regular pentagon to the middle.

Notice that if we draw a circle in the middle of the pentagon we obtain five congruent angles.

Since a circle is 360^(∘), we know that the measure of each angle is equal to 72^(∘). 360^(∘)/5= 72^(∘) Then, if we rotate the pentagon by 72^(∘), it will map onto itself.

The same is true if we rotate the image 144^(∘). Therefore, the correct options are D and G, respectively.