GCSE students need to be able to work out the equation of a graph from what it looks like.

If it’s a straight line graph you just need to look for two things.

1. The Intercept. This is where the line crosses the y axis.

2. The gradient. This is the steepness of the line. If the line goes up from left to right it will be positive. If the line goes down from left to right it will be negative. The larger the number the steeper the line.

This example shows the line y=2x-4. The line goes up two units for each unit it goes across. The gradient is 2÷1=2. It crosses the y axis at -4, so the intercept is -4.

Mathematicians use y=mx+c as the general formula for any straight line. The gradient is m and the intercept is c.

Try this exercise to see if you can match the graphs with their equations.

Try this exercise to see if you can match the equations with the correct gradient and intercept.