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BASIC GEOMETRY 7.1: RATIO & PROPORTION Ratio Compares two numbers by division. Writing ratios a to b a:b a b Slope = ratio of rise/run Write a ratio expressing the slope of l. Extended Ratios Compares more than 2 numbers. Example: For the rectangle, the ratio of the side lengths may be written as 3:7:3:7 Extended Ratio Example The ratio of the side lengths of a triangle is 4:7:5, and its perimeter is 96 cm. What is the length of the shortest side? Proportion Equation stating that two ratios are equal. a c or a:b = c:d Solving Proportions b d a&d are the extremes b&c are the means Use the cross products property (means = extremes) a c → ad = bc b d Hints: When multiplying sums or differences, use parenthesis. Solve each proportion. A) 7 56 x 72 20 B) x 4 5 x4 Equivalent Forms of Cross Products Using Properties of Proportions Given that 18c = 24d, find the ratio of d to c in simplest form. Example Marta is making a scale drawing of her bedroom. Her rectangular room is 12½ feet wide and 15 feet long. On the scale drawing, the width of her room is 5 inches. What is the length? Assignment 1 Page 457 #’s 3-10,14-16,(56)