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Lesson Plans and Worksheets for Geometry

Lesson Plans and Worksheets for all Grades

More Lessons for Geometry

Common Core For Geometry

Student Outcomes

- Students create scale drawings of polygonal figures by the Parallel Method.
- Students explain why angles are preserved in scale drawings created by the Parallel Method using the theorem on parallel lines cut by a transversal.

**Making Scale Drawings Using the Parallel Method**

Classwork

**Opening Exercise**

Dani dilated β³ π΄π΅πΆ from center π, resulting in β³ π΄β²π΅β²πΆβ². She says that she completed the drawing using parallel lines. How could she have done this? Explain.

**Example 1**

a. Use a ruler and setsquare to draw a line through πΆ parallel to π΄π΅. What ensures that the line drawn is parallel
to π΄π΅?

b. Use a ruler and setsquare to draw a parallelogram π΄π΅πΆπ· around π΄π΅ and point οΏ½

**Example 1**

- Create a scale drawing of the figure below using the ratio method about center π and scale factor π = 3/4. Verify that the resulting figure is in fact a scale drawing by showing that corresponding side lengths are in constant proportion and the corresponding angles are equal in measurement.

**Example 2**

Use the figure below with center π and a scale factor of π = 2 and the following steps to create a scale drawing using the parallel method.

Step 1. Draw a ray beginning at π through each vertex of the figure.

Step 2. Select one vertex of the scale drawing to locate; we have selected π΄β². Locate π΄β² on ππ΄ so that ππ΄
β² = 2ππ΄.

Step 3. Align the setsquare and ruler as in the image below; one leg of the setsquare should line up with side π΄π΅, and
the perpendicular leg should be flush against the ruler.

Step 4. Slide the setsquare along the ruler until the edge of the setsquare passes through π΄β². Then, along the
perpendicular leg of the setsquare, draw the segment through π΄β² that is parallel toπ΄π΅ until it intersects with ππ΅, and
label this point π΅β².

Step 5. Continue to create parallel segments to determine each successive vertex point. In this particular case, the
setsquare has been aligned with π΄πΆ. This is done because, in trying to create a parallel segment from π΅πΆ, the parallel
segment was not reaching π΅β². This could be remedied with a larger setsquare and longer ruler, but it is easily avoided by
working on the segment parallel to π΄πΆ instead.

Step 6. Use your ruler to join the final two unconnected vertices.

**Exercises**

- With a ruler and setsquare, use the parallel method to create a scale drawing of ππππ by the parallel method. πβ² has already been located for you. Determine the scale factor of the scale drawing. Verify that the resulting figure is in fact a scale drawing by showing that corresponding side lengths are in constant proportion and that corresponding angles are equal in measurement.
- With a ruler and setsquare, use the parallel method to create a scale drawing of π·πΈπΉπΊ about center π with scale factor π = 1/2. Verify that the resulting figure is in fact a scale drawing by showing that corresponding side lengths are in constant proportion and that the corresponding angles are equal in measurement.
- With a ruler and setsquare, use the parallel method to create a scale drawing of pentagon πππ ππ about center π with scale factor 5/2. Verify that the resulting figure is in fact a scale drawing by showing that corresponding side lengths are in constant proportion and that corresponding angles are equal in measurement.

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