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7.RP.2 & 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?
Was the second photo a reduction or an enlargement of the original picture?
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.
R W P N
* 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.*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.