Find how the perimeter and the area of the figure change when its dimensions change.

8-4 Changing Dimensions: Perimeter and Area

Find how the perimeter and the area of the figure change when its dimensions change.

The original figure is a 4 2 in. rectangle.

The smaller figure is a 2 1 in. rectangle.

Draw a model of the two figures on graph paper. Label the dimensions.

= 1 inch


Additional Example 1 Continued


P = 2(l + w) P = 2(l + w).

Use the formula for perimeter of a rectangle.


Additional Example 1 Continued



Check It Out: Example 1

Find how the perimeter and area of the figure change when its dimensions change.

When the dimensions of the rectangle are multiplied by 2, the perimeter is multiplied by 2 and the area is multiplied by 2 .2

8 in.

4 in.

4 in.

2 in.


Additional Example 2: Application

Draw a rectangle whose dimensions are 4 times as large as the given rectangle. How do the perimeter and area change?

When the dimensions of the rectangle are multiplied by 4, the perimeter is multiplied by 4, and the area is multiplied by 42.

3 cm2 cm

8 cm

12 cm



Draw a rectangle whose dimensions are 2 times as large as the given rectangle. How do the perimeter and area change?

5 cm3 cm

6 cm

10 cm


Check It Out: Example 2 Continued

2

When the dimensions of the rectangle are multiplied by 2, the perimeter is multiplied by 2, and the area is multiplied by 4, or 2 .


Mei works at a local diner whose speciality is making pancakes. She makes silver dollar pancakes with a diameter of 2 inches as well as regular pancakes with a diameter double that of the silver dollar pancakes. Does a regular pancake have twice the area of a silver dollar pancake? Explain. Use 3.14 for .

Find the area of each pancake and compare.


Mei works at a local diner whose speciality is making pancakes. She makes silver dollar pancakes with a diameter of 2 inches as well as regular pancakes with a diameter double that of the silver dollar pancakes. Does a regular pancake have twice the area of a silver dollar pancake? Explain. Use 3.14 for .



Rae is designing a can for a new line of soup products. The original can had a base diameter of 7 cm and her new design will be double that of the original base diameter. Will the new soup can take up double the shelf space of the original can? Explain. Use 3.14 for .

original can base ≈ 38.47 cmnew can base ≈ 153.86 cmNo, the can will take 2 , or four times the shelf space.

2

2

2


Find how the perimeter and area of the triangle change when its dimensions change.


1. Identify how the perimeter and area of the triangle change when its dimensions change.

Lesson Quiz for Student Response Systems

Find how the perimeter and the area of the figure change when its dimensions change.

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