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Proportions & Similar Figures. Less 4-1 Using Proportions. Proportions Review…. What is a ratio? The comparison of two numbers (given as a fraction) What is a proportion? When two ratios are equal to each other How do we solve for a proportion?
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Proportions & Similar Figures Less 4-1 Using Proportions
Proportions Review… What is a ratio? The comparison of two numbers (given as a fraction) What is a proportion? When two ratios are equal to each other How do we solve for a proportion? Use cross products (cross x, cross x, ÷ to solve) How do we use proportions for solving for percentages? **(formula) “is #” = given/missing % “of #” 100%
Proportions & Similar figures • Similar figures = polygons of same shape, different size • Missing sides of similar figures… • …can be solved by proportions • 10 4 • 6 • 15
Proportions & Similar figures In the figure, ▲ABC is similar to ▲DEF. Find the missing length for side DE AB = AC DF DE 15 = 21 10DE DE = 15 • C • E • 21x • 18 • A 15B D 10 F
Proportions & Similar figures In the figure, ▲RST is similar to ▲XYZ. Find the missing length for side XZ Find length XZ • S • 8 4 • R T Z • 10 • X Y 12
Practice In the figure, ▀ ABCD is similar to ▀ QRST. Find the missing length for side QR Find the length QR • A 12 B • 9 • C D • Q R • 3 • S T