Download SimilarTrianglesLesson

Topic: Similar Triangles
Grade/Subject: 9th/10th Geometry
Class Length: 90 minutes
Objective(s): SWBAT
 Find the proportion of corresponding sides of triangles.
 Use AA Similarity to identify congruent triangles.
 Use the isosceles and equilateral triangle theorems to relate sides of a triangle to angles
of a triangle.
Materials Needed:
 60 uniform rubber bands (Engage)
 Tape (Engage)
 Chart paper tablet (Group Activity)
 One bag of candy corn per class (Group Activity)
 One blank piece of butcher paper per student (Engage)
 30 Right-handed candy corn sheets (Engage)
 10 left-handed candy corn sheets (Engage)
 One “Stretching Candy Corn” direction sheet per student (Engage)
 One “Perfect Candy Corn” scenario sheet per student (Group Activity)
Quick Lesson Outline:
1. ENGAGE: Stretching Candy Corn Activity (20 minutes)
2. CLASS DISCUSSION: What did you find? (5 minutes)
3. NOTES: Similar Triangles, AA Similarity (25 minutes)
4. GROUP ACTIVITY: “The Perfect Candy Corn” (30 minutes)
5. SHARE OUT/SUMMARY: What did you find? Why? (10 minutes)
Stretching Candy Corn Activity
Directions: In this activity you will be using rubber bands to enlarge a drawing of a candy corn.
Step One: Create your “Two-band Stretcher” device.
1. Make a two-band stretcher by linking two rubber bands together, as shown.
Step Two: Make your new drawing.
1. Tape the paper with the candy corn on your desk next to the sheet of blank paper.
2. With a pencil-tip or your finger, hold down one end of your stretcher on point P, the anchor
point.
3. Put your pencil in the other end of the stretcher. Stretch the rubber bands with your pencil
until the knot on your two-band stretcher is above the picture you wish to copy.
4. Trace out the new, enlarged candy corn by moving the drawing pencil in such a way that
the know “traces” out the features of the original (*NOTE* Focus on the knot, not your
pencil).
Step Three: Reflect on what you see.
1. Write two sentences comparing your original picture to your new image. What if you used
three rubber bands? What would happen?
2. Measure the lengths of the segments in the original picture and the new picture. How do
they compare?
3. Use the butcher paper to compare the angles you see in the original picture and the new
picture. What do you notice?
Name:_______________________
Period: _____
Stretchy Candy Corn
(Left Handed Version)
P
Name:_______________________
Period: _____
Stretchy Candy Corn
(Right Handed Version)
P
Name: ____________________________
The Perfect Candy Corn
Scenario: The Jelly Belly Candy Company is well known for making some of the best candy corn!
They have always the perfect proportion of yellow, orange, and white on their candy corn.
Unfortunately, the geometric ratio spectrometer at the factory broke! One of the factory workers only
remembers these facts about “the perfect candy corn.”
White
Orange
Yellow
Directions: The Jelly Belly Candy Company needs your help fixing the geometric ratio spectrometer.
With a partner, develop a plan to create the perfect candy corn based on the facts that you know above.
You need to develop your own proportion of sides. Provide an explanation of why you chose the sides
that you did.
Your poster plan needs to include:
 A picture of your perfect candy corn with all sides and angles labeled.
 The proportion that relates the sides of your triangles.
 A 3-5 sentence explanation telling why you chose the side lengths of your “perfect candy corn.”