Mathwords: Equation of a Line

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Equation of a Line

The various common forms for the equation of a line are listed below. In all forms, slope is represented by m, the x-intercept by a, and the y-intercept by b.

Note: The standard form coefficients A, B, and C have no particular graphical significance.

Forms for the Equation of a Line
Slope-intercept	y = mx + b	Used when you have the slope and the y-intercept.
Point-slope	y – y₁ = m(x – x₁)	(x₁, y₁) is a point on the line.
Standard form	Ax + By = C	If possible, A is nonnegative and A, B, and C are relatively prime integers.
Two-intercept		Used when you have both intercepts.
Vertical	x = a	All points have x-coordinate a.
Horizontal	y = b	All points have y-coordinate b.

Movie Clips (with narration)

Horizontal Line: how to find the equation (1.43M)	Vertical Line: how to find the equation (1.46M)
Point and Slope: How to find the equation of a line (4.13M)	Two Points: How to find the equation of a line (5.5M)