2.5.1

Graphs & Proportion

Test yourself

Gradient of a Straight Line Graph

For a straight line graph the gradient is the constant of proportionality k. y = kx.

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y = 2x

  • For every increase in x, y increases by twice that amount.
  • Since it goes through the origin, y is always double x.
  • y is directly proportional to x with k = 2.
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y = 2x + 3

  • This graph shows y = 2x + 3.
  • Every increase in x corresponds to twice that increase in y.
  • y is not directly proportional to x because of the '+ 3'.

Direct and Inverse Proportions as Graphs

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Direct proportion

  • If y and x are directly proportional, the graph of the relationship will be a straight line graph.
  • It must pass through the origin.
  • It could have a negative gradient.
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Inverse proportion

  • If y and x are inversely proportional then the graph is a curved line that never touches the x or y axes.
  • Part of the graph lies in the top right quadrant and part of the graph lies in the bottom left quadrant.

Jump to other topics

1Numbers

2Equations, Formulae & Identities

3Sequences, Functions & Graphs

4Geometry

5Vectors & Transformation Geometry

6Statistics & Probability

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