Equations of other straight line graphs

The equation of a straight line on a graph is made up of a y term, an x term and a number, and can be written in the form of y = mx + c.

  • The slope of the line is known as the gradient and is represented by the value of m in the equation.
  • The point at which the line crosses the y-axis is the value of c in the given equation, and is referred to as the y-intercept.

Examples

Graph with straight lines

All the points that lie on the green line have a y-coordinate that is the same as the x-coordinate, eg:

({-1},~{-1}) and ({2},~{2})

We say that the equation of the line is y = x.

All the points that lie on the purple line have a y-coordinate that is one number higher than the x-coordinate of the same line, eg:

({-3},~{-2}) and ({0},~{1})

In other words, the y-coordinate equals the x-coordinate + 1.

So the equation of the line is y = x + 1.

Question

What is the equation of the line shown below?

Graph with straight lines

The coordinates of the points are ({2},~{4}), ({1},~{2}) and ({-2},~{-4}).

Here, the y value is always twice the x value.

The equation of the line that fits these x and y values is:

y = 2x

Move on to Test
next