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P. 26 #11-15, 23-27, 37, 39, 45, 47.

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Presentation on theme: "P. 26 #11-15, 23-27, 37, 39, 45, 47."— Presentation transcript:

1 p. 26 #11-15, 23-27, 37, 39, 45, 47

2 p. 26 #11-15, 23-27, 37, 39, 45, 47

3 p. 26 #11-15, 23-27, 37, 39, 45, 47

4 1.4 Direct Variation and Proportion
Objectives: Write and apply direct variation equations. Write and solve proportions. Standard: P Analyze a relation to determine whether a direct or inverse variation exists and represent it algebraically and graphically.

5 I. Determine whether each equation describes a direct variation.
y = 2x yes y = ½ x yes y = 2x + 1 no y = 3/x no

6 II. y varies directly as x
II. y varies directly as x. Find the constant of variation, k, and write an equation of direct variation that relates the two variables, y = kx. Ex 1. y = -24 when x = 4 -24 = k (4) k = -6 equation: y = -6x Ex 2. y = -16 when x = 2 - 16 = k (2) k = -8 equation: y = -8x Ex 3. y = 1 when x = ½ 1 = k (1/2) k = 2 equation: y = 2x

7 III. y varies directly as x.
Ex. 1. If y is 2.8 when x is 7, find y when x is - 4. 2.8 = k (7) .4 = k y = .4 (- 4) y = -1.6 Ex. 2 If y is 6.3 when x is 70, find y when x is 5.4. 6.3 = k (70) .09 = k y = .09 (5.4) y = .486

8 III. y varies directly as x.
Ex. 3 If y is -5 when x is 2.5, find y when x is 6. -5 = k (2.5) -2 = k y = -2 (6) y = -12

9 IV. Use a direct variation equation to solve each word problem.
Ex 1. If 6 tickets cost $72, find the cost of 10 tickets. 72 = k (6) 12 = k y = 12 (10) y = 120 Ex 2. If 3 CDs on sale cost $18, find the cost of 12 CDs. 18 = k (3) 6 = k y = 6 (12) y = 72 Ex 3. If 8 sodas cost $3.20, find the cost of 20 sodas. y = 8

10 IV. Use a direct variation equation to solve each word problem.
Ex 4. Each day Jon rides his bicycle for exercise. When traveling a constant rate, he rides 4 miles in about 20 minutes. At this rate, how long would it take Jon to travel 7 miles? Recall that distance, d, rate, r, and elapsed time, t, are related by the equation d = rt.

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12 V. Proportions It is said that if y varies directly with x, then y is
proportional to x. A proportion is a statement that two ratios are equal. A ratio is the comparison of 2 quantities by division. * Cross-Product Property of Property of Proportion

13 V. Proportions The product of the means equals the product of the extremes: ad = bc

14 V. Proportions Ex 2. 3 = x Ex 1. w = 10 5 2 4 12 6 = 5x 12w = 40
5 2 Ex 1. w = 10 6 = 5x 12w = 40 x = 6/5 w = 40/12 w = 10/3

15 V. Proportions Ex 3. 3x –1 = x 2 (3x – 1) = 5x 6x - 2 = 5x x = 2

16 Application - Physics

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18 Lesson Quiz

19 Homework Packet sheet 1.4 OR p. 33 #14-19 and p. 34 # 32-34, #45-48
Quiz on 1.1 – 1.5 this Wednesday


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