Equation of Straight Line

A straight line is the simplest geometrical curve. Every straight line is associated with an equation. To determine the equation of a straight line, two conditions are required.

Slope-Intercept Form

y = mx+ c

where m is the slope of the straight line and c is the y intercept.

Point-Slope Form

y − y₁ = m(x − x₁)

where m is the slope and (x₁, y₁) is the given point.

Two point Form

where (x₁, y₁) and (x₂, y₂) are the two given points.

Intercept Form

where a and b are x and y intercepts respectively.

Normal Form

Equation of a straight line in terms of the length of the perpendicular p from the origin to the line and the angle α which the perpendicular makes with x-axis.

x cos α + y sin α = p

General Form

The equation ax + by + c = 0 always represents a straight line.