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Direct Variation

This topic covers determining whether a data set has direct variation and forming an equation for the variation. It also covers the constant of proportionality (k) and related word problems.

Topic: Determine Direct Variation

  • In direct variation, two variable quantities are related proportionally by a constant positive ratio, e.g. y = kx

  • The ratio is called the constant of proportionality (k)

  • Plot a graph to find the relationship; Straight lines show direct relationships and intercept of the line is zero

  • Direct variation can also be checked by comparing the ratios

Topic: Finding Equations of Direct Variation

  • The equation of direct variation is ‘y = kx’

  • Substitute the values of ‘x’ and ‘y’ in the equation to find the value of ‘k’

  • Substitute the value of ‘k’ in the equation y = kx to find the equation of direct variation

Topic: Word Problems

  • The equation of direct variation is ‘y = kx’

  • Substitute the values of ‘x’ and ‘y’ in the equation to find the value of ‘k’

  • Use ‘y = kx’ to find the missing variable y or x
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