The three co-ordinates are , and . You can find the equation of the straight line using two of these co-ordinates and testing with the final co-ordinate to see if they all lie on the same line.

We have used the co-ordinates and to calculate the gradient and the equation of the straight line so we check whether the other co-ordinate, , fits the line.

When

Therefore the three co-ordinates are , and all lie on the straight line with the equation, .