2.2.4

Finding Equation

Test yourself

Finding the Equation of a Line From a Graph

We can calculate the equation of a line if we have two points on the line or one point and the gradient.

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Given two points - method

  • To find the equation of a line between two points, first calculate the gradient m.
  • Then substitute in one of the points into the equation and rearrange to find c.
  • For example to find the equation of the line between (2,4) and (-1,2)...
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Given two points - step 1

  • Find the gradient:
    • change in y = 4 - 2 = 2
    • change in x = 2 - (-1) = 3
    • so m = 23
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Given two points - step 2

  • We know the line is y = 23x + c so substitute in x = 2 and y = 4 to find c:
    • (4) = 23(2) + c
    • so c = 83
  • Therefore the line is y = 23x + 83.
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Given gradient and point

  • To find the equation of a line with a given gradient and going through a point substitute in the point to the line y = mx + c where m is the gradient you’ve been given.

Jump to other topics

1Number

1.1Place Value

1.2Factors & Multiples

1.3Operations

1.4Fractions, Decimals & Percentages

1.5Growth & Decay

1.6Measurements & Units

1.7Accuracy

2Algebra

3Ratio, Proportion & Rates of Change

4Geometry & Measures

5Probability

6Statistics

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