Section 3.7 Variation

Before Starting this Section, Review

  1. 1 Equation of a line (Section 2.3 , page 201)

  2. 2 Solving linear equations (Section 1.1 , page 83)


  1. 1 Solve direct variation problems.

  2. 2 Solve inverse variation problems.

  3. 3 Solve joint and combined variation problems.

Newton and the Apple

According to legend, Isaac Newton was sitting under an apple tree, and when an apple fell on his head, he suddenly thought of the Law of Universal Gravitation. As in many such legends, the story may not be true in detail, but it contains elements of the truth.

Before we tell you a more realistic version of this story, let’s recall some terminology ...

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