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Year 9 · Functions & Graphs

Equations of straight lines

A straight line can be written y = mx + c: m is the gradient, c is where it crosses the y-axis.

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How to do it

  1. The number in front of x is the gradient.
  2. The number on its own is the y-intercept.
  3. A point is on the line if its coordinates make the equation true.

Worked example

Does the point (1, 10) lie on the line y = 2x + 8?
Substitute x = 1: y = 2 × 1 + 8 = 10, which matches, so yes.
Answer: Yes

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y = x + 4 has gradient 1.

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