You are told that a straight line runs through 2 points: (1,1) and (2,3). What is the equation of the line?

Recall that all straight lines have the general equation y = mx + c, where m is the gradient of the line and c is the y intercept. First work out the gradient, m, of the line: Gradient = rise/run = (change in y)/(change in x): (3-1)/(2-1) = 2/1 = 2Now you know the gradient of the line, you can fill in known x and y values from one of the two points which you are given:3 = (2 x 2) + c ; 3 = 4 + c ; c = -1The equation of the line is therefore: y = 2x -1