Geometry – Chapter 9 Lesson Plans
Section 9.2 – Similar Polygons
Enduring Understandings: The student shall be able to:
- identify similar polygons.
Standards: 23. Similarity
Recognizes and applies properties of similar polygons using ratio and proportion.
Warm up/Opener:
Essential Questions: How can we use proportions to find unknown measures of similar polygons?
Activities:
Lesson/Body:
A polygon is a closed figure in a plane formed by segments called sides. It is a general term used to describe a geometric figure with at least three sides. Polygons that are the same shape but not necessarily the same size are called similar polygons. The vertices of two similar polygons are written in order to show the corresponding parts. The symbol for similar is ~.
Definition of Similar Polygons: Two polygons are similar iff their corresponding angles are congruent and the measures of their corresponding sides are proportional.
Model: see page 356
Symbols: polygon ABCD ~ polygon EFGH – ORDER OF LETTERS IS IMPORTANT. We are saying that angle A is congruent to angle E, etc.
The definition of Similar Polygons can be used to prove two shapes are similar, or used to determine the value of an unknown to make the polygons similar.
The ratio of the lengths of two corresponding sides of two similar polygons is called the scale factor. Scale Drawings are often used to represent something that is too large or too small to be drawn actual size. Contractors use scale drawings, called blueprints, to represent a floor plan of a house. The blueprint and floor plan are similar polygons.
Assessments:
CW WS 7.2 of the red book
CW WS 9.2 of the blue book
HW pg 359-361, # 9 – 27 odd, (10)
Assign scale drawing project
Scale Drawing Project
Select a small drawing of your choice. It can be from the comics, coloring book, magazine, or one that you have drawn. Mark a grid over the drawing, using a minimum of five (5) horizontal and five (5) vertical lines crossing your drawing. The lines must be equally spaced, and should be a standard measure, for example, ¼ of an inch.
Determine a scale factor, and draw a new grid on another piece of paper multiplied by the scale factor. Transfer the intersection points of the original drawing to the new grid and add the connecting lines to complete the drawing. The project can be in black and white, but color makes it more interesting.
Deliverable – THIS IS FOR A QUIZ GRADE:
1. Due at the beginning of your class on 1/15 or 1/16. (5 points)
2. The original drawing with grid lines shown. (5 points)
3. The new drawing to the new scale factor. (20 points)
4. Neatness and accuracy of project. (10 points)
5. The scale factor shown on the new drawing. (5 points)
6. Total points: 45 points
Scale Drawing Project
Select a small drawing of your choice. It can be from the comics, coloring book, magazine, or one that you have drawn. Mark a grid over the drawing, using a minimum of five (5) horizontal and five (5) vertical lines crossing your drawing. The lines must be equally spaced, and should be a standard measure, for example, ¼ of an inch.
Determine a scale factor, and draw a new grid on another piece of paper multiplied by the scale factor. Transfer the intersection points of the original drawing to the new grid and add the connecting lines to complete the drawing. The project can be in black and white, but color makes it more interesting.
Deliverable – THIS IS FOR A QUIZ GRADE:
1. Due at the beginning of your class on 1/15 or 1/16. (5 points)
2. The original drawing with grid lines shown. (5 points)
3. The new drawing to the new scale factor. (20 points)
4. Neatness and accuracy of project. (10 points)
5. The scale factor shown on the new drawing. (5 points)
6. Total points: 45 points