1. Copyright © by Holt, Rinehart and Winston. All Rights Reserved. Objectives Write and apply direct-variation equations. Write and solve proportions. 1.4 Direct Variation and Proportion

2. Copyright © by Holt, Rinehart and Winston. All Rights Reserved. Glossary Terms constant of variation Cross-Product Property of Proportions direct variation proportion 1.4 Direct Variation and Proportion

3. Copyright © by Holt, Rinehart and Winston. All Rights Reserved. Rules and Properties Direct Variation y = kx is called a direct-variation equation. k is the constant of variation. 1.4 Direct Variation and Proportion k  0

4. Copyright © by Holt, Rinehart and Winston. All Rights Reserved. Rules and Properties Cross-Product Property of Proportions 1.4 Direct Variation and Proportion If, then ad = bc. = a b c d For b  0 and d  0:

5. Copyright © by Holt, Rinehart and Winston. All Rights Reserved. Key Skills Write a direct-variation equation for given variables. 1.4 Direct Variation and Proportion k = 5 27 = 5.4 y = 5.4x Find the direct-variation equation for y = 27 when x = 5.

6. Copyright © by Holt, Rinehart and Winston. All Rights Reserved. 35x = 350 Key Skills Write and solve proportions. 1.4 Direct Variation and Proportion x x x = 10 35 87.5 350 4 35 4 87.5 x = TOC