# Unit 6: Scale Factor and Measurement How will you measure up?

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Unit 6: Scale Factor and Measurement How will you measure up?

Similar figures What am I Learning Today? How will I show that I learned it? Demonstrate the relationship between similar plane figures using ratio and proportion Use proportions to find missing measures in similar figures Solve problems using proportions

Vocabulary Corresponding: The relationship between the sides and angles of two or more objects that are matched Corresponding: The relationship between the sides and angles of two or more objects that are matched Similar: Figures with the same shape, but not necessarily the same size Similar: Figures with the same shape, but not necessarily the same size Congruent: Figures that have the same size and shape Congruent: Figures that have the same size and shape

Matching sides of two or more polygons are called corresponding sides, and matching angles are called corresponding angles.

What do you remember about Ratio and Proportion? See if you can answer these… 1) What is a ratio? A comparison of two quantities measured in the same units 2) What is a proportion? An equation that shows two ratios are equivalent 3) Explain how you find a missing value in a proportion. Find the cross products. Isolate the variable using the inverse operation.

Questions Notes Questions Answers How do I know two figures are similar? What is a tic- tac-toe grid? 1) The measure of the corresponding angles are equal 2) The ratios of the lengths of the corresponding sides are proportionate How can I find the length of a missing side of similar figures? 1) Write a proportion using corresponding sides 2) Use a tic-tac-toe grid to help set up the proportion correctly. 3) Solve proportion using cross product. L1 L2 W1 W2 = or L1 W1 L2 W2 = For example, ratios should be set up to compare length to length and width to width, which puts the first shape as both numerators and the second as both denominators. OR Ratios should compare a shape’s length to its width, which gives each shape its own ratio.

Similar Figures Figures that have the same shape, but may not be the same size. They also do not have to be in the same position. Matching sides are proportional Matching angles have the same measure. 3 5 4 9 15 12 3 3 3 3 8 6

52 y ___ 50 100 ____ = Write a proportion using corresponding side lengths. The cross products are equal.100 52 = 50 y A B 60 m 120 m 50 m 100 m y 52 m The two triangles are similar. Find the missing length y. y is multiplied by 50. 5,200 = 50y Divide both sides by 50 to undo the multiplication. 5,200 50 _____ 50y 50 ___ = y =104 meters

54 3 = 2 w 162 = 2w 162 2 ____ 2w 2 ___ = 81 = w The width of the actual painting is 81 cm. Write a proportion. The cross products are equal. w is multiplied by 2. Divide both sides by 2 to undo the multiplication. 3 cm w cm 2 cm 54 cm _____ = This reduction is similar to a picture that Katie painted. The height of the actual painting is 54 centimeters. What is the width of the actual painting?

Let’s Practice http://www.harcourtschool.com/activity/similar_congruent/ http://www.quia.com/rr/232263.html?AP_rand=243379547

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