Straight-line graphs

A straight line has the equation y = mx + c. m is how steep it is (the gradient), c is where it crosses the y-axis.

Key facts

  • Gradient = change in y ÷ change in x.
  • c is the y-intercept.
  • Two lines cross where their y values are equal.

Worked examples

Example 1

Where do y = 2x − 1 and y = −x + 5 cross?

  1. At the crossing, the y values match. 2x − 1 = −x + 5
  2. Add x, add 1. 3x = 6, x = 2
  3. Put it back in. y = 2 × 2 − 1 = 3

Answer: (2, 3)

Questions about straight-line graphs