Transcript 2.8 – Proportions & Similar Figures

2.8 – Proportions & Similar
Figures
“I can solve proportions using scale
factors.”
“I can find missing side lengths of
similar figures.”
VOCABULARY
1. Similar Figures - Figures that are the same shape,
but not the same size. Corresponding angles are
equal, but the corresponding sides are
proportional.
2. Scale – the ratio of any length on a drawing to the
actual length
Similar Figures
This symbol
means
“similar to”
The ratios of all
3 sides are the
exact same
Each angle is equal to another angle in
the same position in the other triangle.
Find the missing sides
lengths, a and b.
First, write a ratio you know
8 .
6.4
Next, write a proportion with a
side length you need to find.
8 = 7 .
6.4
a
Last, Cross multiply and solve!
8a = 44.8
a = 5.6
Find length
b on your
own
The sun’s rays strike the building and
the girl at the same angle, forming
two similar triangles. How tall is the
building if the girl is 5ft?
girl’s shadow = building’s shadow
girl’s height
building’s height
3 = 15
5
x
3x = 75
x = 25
The building
is 25 feet
tall.
-3ft-
-------15ft--------
Class work/Homework
• You are to complete the Mirror Open
Response before you leave.
– If you do not finish it, it is homework.
• Your homework is p. 134 # 6 – 18 (even)