Perimeters and Areas of Similar Figures

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Perimeters and Areasof Similar Figures

• 11.3

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ReminderTheorem 8.1

• If two polygons are similar, then the ratio of
  their perimeters is equal to the ratios of their
  corresponding side lengths.

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Theorem 11.5Areas of Similar Polygons

• If two polygons are similar with the lengths of
  corresponding sides in the ratio of ab, then the
  ratio of their areas is a²b²
• Side Length of A a
• Side Length of B b
• Area of A a²
• Area of B b²

a
b
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Example

• Pentagons ABCDE and LMNPQ are similar.
• Find the ratio (red to blue) of
• the areas.

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Example

• A regular octagon has a side length of 16 ft. and
  an area of 512 ft.². Find the area of a smaller
  regular octagon that has a perimeter of about 80
  ft.

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Homework

• Pg. 679
• 7-10, 19-20

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Example

• Pentagons ABCDE and LMNPQ are similar.
• Find the ratio (red to blue) of
• the areas.