1-5 Using Formulas in Geometry
Bellwork
Write a definition of the angle pairs below,
and draw a diagram to represent each
pair.
Holt McDougal Geometry
1-5 Using Formulas in Geometry
Rigor
Apply formulas for perimeter, area, and
circumference.
Relevance
Formulas help determine the amount
needed and cost of materials.
Holt McDougal Geometry
1-5 Using Formulas in Geometry
The perimeter (P) is the sum of the
side lengths of the figure. Units for
length (ft, m, in)
The area (A) is the number of
square units of a given size that
exactly cover the figure. Square
units (ft2, m2, in2)
Holt McDougal Geometry
1-5 Using Formulas in Geometry
Rectangle
Triangles
Circles
h
b
A = bh
b=base,
h=height
Holt McDougal Geometry
A = ½ bh
A = r2
Circumference (C)
C = 2r C = d
r = radius
d = diameter
1-5 Using Formulas in Geometry
The base b can be any side of a
triangle.
The height h is a segment from a
vertex that forms a right angle with a
line containing the base.
Holt McDougal Geometry
1-5 Using Formulas in Geometry
Example 1: Finding Perimeter and Area
Find the perimeter and area of each figure.
Holt McDougal Geometry
1-5 Using Formulas in Geometry
Example 2: Crafts Application
The Texas Treasures quilt block includes 24
purple triangles. The base and height of each
triangle are about 3in. Find the approximate
amount of fabric used to make the 24 triangles.
If the fabric costs $8 per square
foot, how much will the fabric
cost?
Holt McDougal Geometry
1-5 Using Formulas in Geometry
Example 3: Calculate the Circumference and
Area of a Circle
Calculate C and A of the 12in pizza in terms of 
and to the nearest tenth.
Holt McDougal Geometry
1-5 Using Formulas in Geometry
Composite Figures
• Composite figure– a region made of
common, non-overlapping shapes
• Area Addition Postulate – the area of a
region is the sum of the areas of its nonoverlapping parts
Holt McDougal Geometry
1-5 Using Formulas in Geometry
Example 4: Calculate the area of the shaded regions
below.
Holt McDougal Geometry
1-5 Using Formulas in Geometry
Example 5: Real Life Application
A) If a runner were to run 4 laps on the outer
track, about how far would he run? Use 3.14
for .
B) The school re-sods the grass inside the
track. About how many square feet should
the school buy? Use 3.14 for .
Holt McDougal Geometry
1-5 Using Formulas in Geometry
Classwork from the Textbook
Heading: Section 1-5 Classwork pg 38-39
Assignment:
pg 38 #3 – 9
pg 39 #20 – 22, 26, 30
Homework from the Core Book
Core book 1-5 Problem Solving: pg 30 #1 – 6
Due Thursday for periods 1, 3, & 5
Due Friday for periods 2, 4, & 7
Holt McDougal Geometry