1.3 Using Formulas1.3 Using Formulas

GeometryGeometry

Perimeter

• Measures the distance around the edge of any flat object.

• To find the perimeter of any figure, ADD the lengths of its sides.

What is a rectangle?

A rectangle has:

4 sides

4 square corners or right angles

Opposite sides are of equal lengths

Opposite sides are directly across from each other

To find the perimeter of a rectangle:

18

15

Use the formula

P= 2 x length + 2 x widthP= 2 x 18 + 2 x 15P= 36 + 30= 66

Or …….You can always add the sides.P= 18 + 18 +15 +15= 66

To find the perimeter of a rectangle:

18

15

Use the formula

P= 2 x length + 2 x widthP= 2 x 18 + 2 x 15P= 36 + 30= 66

Or …….You can always add the sides.P= 18 + 18 +15 +15= 66

The area of a shape is a measure of how much surface the shape takes up.

Area

For example, which of these rugs covers a larger surface?

Rug A

Rug B

Rug C

Area of a rectangle

Area is measured in square units.

For example, we can use mm2, cm2, m2 or km2.

The 2 tells us that there are two dimensions, length and width.

We can find the area of a rectangle by multiplying the length and the width of the rectangle together.

length, l

width, w

Area of a rectangle

= length × width

= lw

Area of a rectangle

What is the area of this rectangle?

8 cm

4 cm

Area of a rectangle = lw

= 8 cm × 4 cm

= 32 cm2

A Real Life Example

• Seth is putting carpet in a bedroom that measures 14 ft by 12 ft. How many square feet of carpet does Seth need?– What do you know?

• The dimensions of the room is 14 ft by 12 ft.– l = 14 ft– w = 12 ft

• A = l x w– A = 14 ft x 12 ft– A = 168 ft2

• Seth needs 168 ft2 of carpet.

Practice

Practice