Direct Variation or "is proportional to"

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  • Straight Line Graphs

Class: Form 4 or 5

Duration: A double period (90 mins)

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At the end of this lesson the student should be able to:
  1. Make real life connections between two variables.
  2. Show how well known mathematical formulae were derived using the concept of variation eg. circumference, area etc.
  3. Recognise the symbol for proportionality ; .
  4. Find the constant of variation given data.
  5. Give the formula connecting both variables (having found the constant of variation).
  6. Evaluate one of the variables once the data for the other variable is given.
  7. Draw a graph the relation, plotting one variable against the other

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Direct Proportionality

Two quantities x and y are said to be related by a direct proportionality if an increase in x by a factor will lead to an increase in y by exactly the same factor.