HONORS GEOMETRY
7.3. Similar Triangles
Do Now:
• 1. An electronics company manufactures widescreen
television sets in several different sizes. The rectangular
viewing area of each television size is similar to the
viewing area of the other sizes. The company’s 42 inch
widescreen television has a viewing area perimeter of
approximately 144.4 inches. What is the viewing area
perimeter of the company’s 46 inch widescreen
television?
• 2. An official Olympic-sized ice hockey rink measures 30
meters by 60 meters. The ice hockey rink at the local
community college measures 25.5 meters by 51 meters.
Are the ice hockey rinks similar? Why or why not?
Homework
• Comments?
• Questions?
• Concerns?
• Confusions?
• ASK ASK ASK ASK!
Angle-Angle (AA) Similarity
• If two angles in one triangle are congruent to two angles
of another triangle, then the triangles are similar.
• **Note: By what theorem would the third angles be
congruent?
Example One:
You Try!
• Are the following triangles similar? If yes write a similarity
statement. Explain your reasoning.
Side- Side- Side (SSS) Similarity
• If the corresponding side lengths of two triangles are
proportional, then the triangles are similar
• **Warning: This is not SSS which proves two triangles are
congruent, this is SSS similarity.
Side- Angle- Side (SAS) Similarity
• If the lengths of two sides of one triangle are proportional
to the lengths of two corresponding sides of another
triangle, and the included angles are congruent, then the
triangles are similar.
• **Warning: This is not SAS which proves two triangles are
congruent, this is SAS similarity.
Example Two:
• Are the following triangles similar? If so, write a similarity
statement. Explain your reasoning.
Example Three:
You Try!
• Are the following triangles similar? If so, write a similarity
statement. Justify your reasoning.
Example Four:
• If the given triangles are similar, find the missing variables
Example Five:
• If the given triangles are similar, find the missing
variables.
You Try!
• Find the missing variables if the triangles are similar.
Example Six:
Example Seven:
You Try!
• A cell phone tower casts a 100 foot shadow. At the same
time a 4 foot 6 inch post near the tower casts a shadow of
4 feet 4 inches. Find the height of the tower.
• **Warning: Watch your units!***
Practice Problems
• Try some on your own/in your table groups
• As always don’t hesitate to ask me questions if you are
confused! Or talk to a table mate– that’s what they are
here for!
Exit Ticket