Area and Perimeter of Similar Figures

Lesson #6Pg. 147

What you will learn…

• The perimeters of similar figures are related by the scale factor

• The areas of similar figures are related by the square of the scale factor

Perimeter and Area of Similar Figures

Perimeter

Words - If figure B is similar to figure A by a scale factor, then the perimeter of B is equal to the perimeter of A times the scale factor

Symbols –

Models

Figure A

Figure B

Area

Words - If figure B is similar to figure A by a scale factor, then the Area of B is equal to the Area of A times the square of the scale factor

Symbols –

Perimeter of figure B

Perimeter of figure A (𝑆𝑐𝑎𝑙𝑒 𝐹𝑎𝑐𝑡𝑜𝑟 )

Area of figure B

Area of figure A (𝑆𝑐𝑎𝑙𝑒 𝐹𝑎𝑐𝑡𝑜𝑟 )2

Perimeter Example

• Two rectangles are similar. One has a length of 6in. And a perimeter of 24 in.. The other has a length of 7 in..– What is the perimeter of this rectangle?

• Draw picture

Perimeter Example• Triangle LMN is similar to triangle PQR. If the

perimeter of triangle LMN is 64 meters, what is the perimeter of triangle PQR?

Perimeter Example• In a scale drawing, the perimeter of the

garden is 64 in.. The actual length of AB is 18ft.. – What is the perimeter of the actual garden?

• Always convert to same units

• Find the scale factor

• Find the perimeter of the actual garden

Perimeter Example• Two quilting squares are shown. The scale

factor is 3 : 2. – What is the perimeter of square TUVW?

Area Example• The Eddington’s have a 5x8 ft. porch on the

front of their house. They are building a similar poarch on the back with double (SF) the dimensions. – What is the area of the back porch?

HomeworkAll: pg. 151-152

(1-7, 9, 10)Test Tuesday

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