Cambridge O Level Additional Mathematics · Syllabus 4037 · Straight-Line Graphs
Equation of a Straight Line
What is Equation of a Straight Line?
The equation of a straight line is a relation between x and y satisfied by every point on the line and by no other point. The same line can be written in several equivalent forms: gradient-intercept form y = mx + c, which displays the gradient m and the value of y where the line crosses the vertical axis; point-gradient form y - y1 = m(x - x1), which is used as soon as a gradient and one point are known; and the general form ax + by = c, which has integer coefficients and no fractions. Horizontal lines take the form y = k and vertical lines the form x = k, and a vertical line cannot be written as y = mx + c because its gradient does not exist.
This definition is part of the Straight-Line Graphs chapter in Cambridge O Level Additional Mathematics.