Holt Algebra Direct Variation Use a graph of the function to find the value of f(x) when x = –4. Check your answer.

Holt Algebra Direct Variation Identify, write, and graph direct variation. Objective

Holt Algebra Direct Variation A recipe for paella calls for 1 cup of rice to make 5 servings.

Holt Algebra 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.

Holt Algebra Direct Variation Tell whether each equation represents a direct variation. If so, identify the constant of variation. y = 3x 3x + y = 8 –4x + 3y = 0

Holt Algebra Direct Variation Tell whether each equation represents a direct variation. If so, identify the constant of variation. 3y = 4x + 1 3x = –4y

Holt Algebra Direct Variation So, in a direct variation, the ratio is equal to the constant of variation. What happens if you solve y = kx for k?

Holt Algebra Direct Variation Tell whether the relationship is a direct variation. Explain.

Holt Algebra Direct Variation Tell whether each relationship is a direct variation. If it is, explain.

Holt Algebra Direct Variation The value of y varies directly with x, and y = 3, when x = 9. Find y when x = 21.

Holt Algebra Direct Variation A group of people are tubing down a river at an average speed of 2 mi/h. Write a direct variation equation that gives the number of miles y that the people will float in x hours. Then graph. distance (mi)

Holt Algebra Direct Variation The perimeter y of a square varies directly with its side length x. Write a direct variation equation for this relationship. Then graph. HW pp /11-43 Odd,46-55 Perimeter