1-5 Using Formulas in Geometry
 The
student will be able to :
 Apply formulas for the perimeter, area and
circumference of a circle.
 What
is perimeter?
 Answer: is the sum of all the sides lengths of
a figure.
 What is area?
 Area is the space inside a two-dimensional
figure.
 What are some of the difference you see
between area and perimeter?
Just remember!!!
Perimeter is expressed in linear units,
such as inches (in.) or meters (m).
Area is expressed in square units,
such as square centimeters (cm2).
 Find
the area and perimeter of each figure:
= 2(6) + 2(4)
= 12 + 8 = 20 in.
= (6)(4) = 24 in2
 Find
the area and perimeter of each figure:
24
13
15
 Solution:
 𝐴𝑟𝑒𝑎
=
 𝐴𝑟𝑒𝑎
=
𝑏𝑎𝑠𝑒∗ℎ𝑒𝑖𝑔ℎ𝑡
2
15∗13
= 97.5
2
 𝑝𝑒𝑟𝑖𝑚𝑒𝑡𝑒𝑟
= 𝑎 + 𝑏 + 𝑐 = 15 + 13 + 24 = 52
 Lets
do the worksheet on area
 The
area of a rectangular fence is 256 𝑓𝑡 2 . If
the height of the fence is 11feet . What is
the base of the fence.
 Solution:
 𝐴𝑟𝑒𝑎 𝑜𝑓 𝑓𝑒𝑛𝑐𝑒 = 𝑏𝑎𝑠𝑒 ∗ ℎ𝑒𝑖𝑔ℎ𝑡
 256 = 11 ∗ 𝑥 then solve for x
256

11
𝑥
=
11𝑥
11
= 23.3 𝑓𝑒𝑒𝑡








The sides of a triangle are (x+5), (3x+5), and (2x4).Find x when the perimeter of the triangle is 60.
Solution:
𝑝𝑒𝑟𝑖𝑚𝑒𝑡𝑒𝑟 = adding all the sides of the triangle
60 = 𝑥 + 5 + 3𝑥 + 5 + 2𝑥 − 4
60 = 𝑥 + 3𝑥 + 2𝑥 + 5 + 5 − 4
60 = 6𝑥 + 6
−6 =
−6
54 = 6𝑥
54

6

=
6𝑥
6
9=𝑥
=
Write and solve the following:
 The length of a rectangle is 5 inches less
than three times its width.
The perimeter is 86 inches. Find the length
and width.
 As shown in the following diagram, a
rectangle's length is 2x + 1 and its width
is 2x – 1. If its area is 15 cm2, what are the
rectangle's dimensions and what is its
perimeter?


 What
is the diameter of a circle?
 Answer: is a segment that passes through the
center of the circle and whose endpoints are
on the circle.
 What is the radius of the circle?
 Answer: is a segment whose endpoints are
the center of the circle and a point on a
circle.
 What
is the circumference?
 Answer: Is the distance around the circle.

The ratio of a circle’s circumference to its
diameter is the same for all circles. This
ratio is represented by the Greek letter 
(pi). The value of  is irrational. Pi is often
approximated as 3.14 or 22/7 .
What is the area of the circle ?
 Answer: is the space inside the circle.

 Find
the circumference and area
of a circle with radius 8 cm. Use
the  key on your calculator.
 Then round the answer to the
nearest tenth.
 50.3 cm
201.1 cm2
 Find
the circumference and area
of a circle with diameter 14m.
 Lets
do the worksheet on area and
circumference.
 Lets
do problems 20-26 and 28.
 From page 39
 Today
we learned about the areas of
difference shapes as well as the
circumference of the circle.
 Tomorrow we are going to continue with 1.6