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Warm-Up • Solve each equation for x. 1) 3x = 5 2) 2x – 1 = 10 3) 5x + 3x = 14 Geometry 7-1 Ratios and Proportions Definition • A ratio compares two numbers by division. • Ratios can be written 3 ways: 1) a to b 2) a : b 3) – b cannot equal zero because you can’t divide by 0 – The first number in “a to b” goes in the numerator of the fraction Additional Note on Ratios A ratio can involve more than two numbers. For the rectangle, the ratio of the side lengths may be written as 3:7:3:7. Example 1 Write a ratio expressing the slope of l. Example 2 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? Example 3 The ratio of the angle measures in a triangle is 1:6:13. What is the measure of each angle? Definition • A proportion is an equation stating that two ratios are equal. • Solve proportions using cross multiplication. Examples • Solve each proportion. • 1) • 2) Re-Writing Proportions Examples 1) Given that 18c = 24d, find the ratio of d to c in simplest form. 2) Given that 16s = 20t, find the ratio s:t in simplest form.