USING FORMULAS IN GEOMETRY

Geometry CP1 (Holt 1-5) K. Santos

Area

Area (A) is the number of nonoverlapping square units of a given size that exactly cover the figure

A = 36 square units

A = 18 square units

A = 7 square units

A = ????? 14 ????

-10

-8

-6

-4

-2

0

2

4

6

8

10

-10 -8 -6 -4 -2 0 2 4 6 8 10

Area of Rectangle

Area = product of its base and height

b

A= bh h

3 ft

5 ft

A = 3(5)

A = 15 square ft

or

A = 15

Area of a Square

Area = product of its base and height

A= bh

6 in

A = 6(6)

A = 36

Area of a Triangle

Area = one half of the product of its base and height

A= bh or A = Base perpendicular to height

h h h

b b b

If b = 4” and h = 6”

Then A = (4)(6)

A = (24)

A = 12

Example—finding a side

The area of a triangle is 24 and its height is 3 cm. Find the length of its corresponding base.

A = for a triangle

24=

48 = 3b

b = 16 cm

Perimeter

Perimeter (P) of a plane figure is the sum of the side lengths of the figure

P = 24

P= 18

P = 16

P= ?-10

-8

-6

-4

-2

0

2

4

6

8

10

-10 -8 -6 -4 -2 0 2 4 6 8 10

Perimeter Formulas

Rectangle: l

P = 2l + 2w w

Square:

P = 4s s

Triangle:

P = a + b + c

a b

c

Circle Formulas

8 ft

r = 4 ft

Area:

A =

A = 16

Circumference:

C = 2r or C =

C = 8 ft