1. Algebra 1 Section 4.2 Slope and Direct Variation

2. Vocabulary: What is a direct variation? What is the constant of variation? An equation in the form y= kx where k ≠ 0 Which represents a constant rate of change. The graph of y = kx always passes through the origin. k is the constant of variation The slope is positive if k > 0.The slope is negative if k < 0.

3. Example 1: Write and solve a direct variation. Suppose y varies directly as x, and y = 28 when x = 7. a.Write a direct variation equation that relates x and y. Step 1 Find the value of k y = kx Direct variation formula 28 = k7 Replace y with 28 and x with 7 28 = k7 Divide both sides by 7 7 7 7 = k Simplify Step 2 Rewrite the direct variation y = kx Direct variation formula y = 7k Replace k with 7 from above

4. Example 2: Suppose y varies directly as x and y = 6 and x = -18. Write a direct variation that relates x and y. Then solve. a.Write a direct variation equation that relates x and y. b.Find y when x = -2

5. Homework Section 4.2 pgs 200-201 12-25, 34-37