1. Chapter 4
4-5 Direct variation

2. Objectives
Identify, write, and graph direct variation.

3. Direct variation
A recipe for paella calls for 1 cup of rice to make 5 servings. In other words, a chef needs 1 cup of rice for every 5 servings.
The equation y = 5x describes this relationship. In this relationship, the number of servings varies directly with the number of cups of rice.

4. Direct variation
A direct variation is a special type of linear relationship that can be written in the form y = kx, where k is a nonzero constant called the constant of variation.

5. Example #1
Tell whether the equation represents a direct variation. If so, identify the constant of variation.
A) y = 3x
B) 3x + y = 8
C) y + 3x = 0

6. Student guided practice
Do problems 2-4 in your book page 263

7. Example#2
Tell whether the relationship is a direct variation. Explain.

8. Example#3
Tell whether the relationship is a direct variation. Explain.

9. Student guided practice
Do problem 5 and 6 in your book page 263

10. Example#4
The value of y varies directly with x, and y = 3, when x = 9. Find y when x = 21.

11. Example#5
The value of y varies directly with x, and y = 4.5 when x = 0.5. Find y when x = 10.

12. Student guided practice
Do problems 7 and 8 in your book page 263

13. Discovery activity
Let’s get into groups and do thediscovery activity

14. Homework
Do problems in your book page 263and 264