At the end of this lesson, students should be able to:
Express direct variation in algebraic terms and use this to form expressions to find unknown quantities.
Know and use the constant of proportionality or constant of variation.
Lesson Content
Direct variation means the same as direct proportion. There is direct variation (or direct proportion) between two variables when one variable is a simple multiple of the other. That is, their ratio is a constant. • x varies as y
• x varies directly as y
• x is proportional to y
These three all mean the same and they are written in symbols as follows.
x ∝ y. The ‘∝’ sign can always be replaced by ‘=k’ where k is a constant equal to the gradient of the graph and it is called the constant of proportionality or constant of variation.
4.7
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