I can ~ find the unit rate as the scale factor. 7.G.1 I can ~ compare, create, and match corresponding figures in scale drawings. I can ~ find the unit rate as the scale factor.

Can you guess the image? 1966 Shelby GT Mustang 1:24 model

Was the top photo a reduction or an enlargement of the original item Was the top photo a reduction or an enlargement of the original item? How do you know?

How about this image?

Was the second photo a reduction or an enlargement of the original picture? How do you know?

Scale drawing: A reduced or enlarged two-dimensional drawing of an original two-dimensional drawing.

P N R W

Why doesn’t point V correspond to point R * Why doesn’t point V correspond to point R? * What must we consider before we identify corresponding points?

Exploratory Challenge: Make your own scale drawing. *Notice the grids are either enlarged or reduced in size. *You are to create a scale drawing on each of the grids. *Will you need to adjust the number of units on each part of the robot? *What is the importance of matching corresponding points? *How can you check the accuracy of your scale drawing?

Do your scale drawings look like this?

Now look at the second set of drawings. Fill in the table to the right *Now look at the second set of drawings. *Fill in the table to the right. *What do you notice about the information in the table? *Does a constant of proportionality exist? How do you know? *What is the constant of proportionality? *If there was no constant, would the drawings be proportional? 18 6 9 3

Now work on the next set of drawings on your own… Does a constant of proportionality exist? Is Luca’s enlarged mosaic a scale drawing of the first image? Why or why not?

Steps to check proportionality: Measure the lengths of the scale figure. Measure the corresponding lengths of the actual figure. Check for a constant of proportionality.

Are the cubes proportional?

What about the app icon?

Notes: Scale drawing: A drawing in which all lengths between points or figures in a drawing are proportional to the actual picture. Reduction: The lengths in the scale drawing are smaller than the actual drawing. Enlargement: The lengths in the scale drawing are larger than the actual drawing. One-to-one Correspondence: Each point in one figure corresponds to one and only one point in the second figure.

Now, let’s practice with scale factor! 

Practice check

Questions?

Exit Ticket: Hayden likes building radio-controlled sailboats with her father. One of the sails, shaped like a right triangle, has side lengths measure 6 inches, 8 inches, and 10 inches. To log her activity, Hayden creates and collects drawings of all the boats she and her father built together. Using the scale factor of ½ , write the dimensions of the reduced sail.