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Geometry
February 13, 2017
7.1 Ratios and Proportions
DO NOW
Solve for x:
1. 5𝑥 = 40
2.
3.
𝑥
7
1
2
=4
=
𝑥
8
Chapter Objective
I can explore scale
factors and similar
polygons.
Today’s Objectives
1. Discuss/review ratios and proportions
Ratio
A comparison of two values representing
relative size of two values:
𝑎
𝑎∶𝑏
𝑎 to 𝑏
𝑏
Ratio
Ex. Jalel is planting a garden. Jalel wants two roses for
every three carnations. If he buys 20 rose plants, how
many carnations should he buy?
Ratio
Ex. If Jalel wants a total of 60 plants, how many of each
should he buy?
Extended ratio
An extended ratio compares three or more values.
Ex. If a triangle’s sides are in the ratio 3 : 4 : 5, it is a
right triangle. If such a triangle has a short leg of 15,
what is the length of its hypotenuse?
Proportion
An equation involving two or more equal ratios
(equivalent fractions).
3 6 12
= =
4 8 16
Cross Products
You can solve proportions for missing values by crossmultiplying.
𝑥 6
=
4 8
⇒ 8𝑥 = 6 ⋅ 4 = 24
24
⇒𝑥=
=3
8
Practice (Worksheet)