Direct Variation and Proportion Objective: Write and apply direct variation and proportion problems
Direct Variation The variable y varies directly as x if there is a nonzero constant k such that y = kx. The equation y = kx is called a direct variation equation and the number k is called the constant of variation.
Example 1 Find the constant of variation, k and the direct variation equation if y varies directly as x and y = -24 when x = 4.
Example 1 Find the constant of variation, k and the direct variation equation if y varies directly as x and y = -24 when x = 4. Use the direct variation equation Substitute -24 for y and 4 for x
Example 1 Find the constant of variation, k and the direct variation equation if y varies directly as x and y = -24 when x = 4. Use the direct variation equation Substitute -24 for y and 4 for x Solve for k.
Example 1 Find the constant of variation, k and the direct variation equation if y varies directly as x and y = -24 when x = 4. Use the direct variation equation Substitute -24 for y and 4 for x Solve for k. The direct variation equation is
Try This Find the constant of variation, k and the direct variation equation if y varies directly as x and y = 21 when x = 7.
Try This Find the constant of variation, k and the direct variation equation if y varies directly as x and y = 21 when x = 7. Use the direct variation equation Substitute 21 for y and 7 for x Solve for k. The direct variation equation is
Example 2 Each day John rides his bike for exercise. When traveling at a constant rate, he rides 4 miles in about 20 minutes. At this rate, how long would it take John to travel 7 miles?
Example 2 Each day John rides his bike for exercise. When traveling at a constant rate, he rides 4 miles in about 20 minutes. At this rate, how long would it take John to travel 7 miles?
Example 2
Proportions A ratio is a comparison of two numbers by division. A proportion is a statement that two ratios are equal.
Proportions A ratio is a comparison of two numbers by division. A proportion is a statement that two ratios are equal. A proportion of the form can be rearranged like this:
Cross-Product Property The result of what we just did is called the cross-product property of proportions. This is also called the means-extremes product property.
Physics Application
Example 3
Example 3
Example 3
Example 4
Example 4
Class work In pairs/groups Page 33 8-13
Homework Pages 33-34 15-25 odd 37-51 odd