# Line

Basics

A line is a flat straight figure extending infinitely through two points.  (See Line L above.)
x-axis = horizontal
x = horizontal coordinate
(x, y) = point representing horizontal and vertical coordinates on Line L

Slope refers to the steepness of a line.
m = slope

Formulas (Mathematics Formula Sheet)
s
lope of a line
m = $\bf\displaystyle\frac{{{y}_{2}}-{{y}_{1}}}{{{x}_{2}}-{{x}_{1}}}$

slope-intercept form of the equation of a line
y = mx + b

point-slope form of the equation of a line
y – y1 = m(x – x1)

Formulas (NOT on Mathematics Formula Sheet)

slope as change
m = $\bf\displaystyle\frac{change\hspace{0.1cm}in\hspace{0.1cm}y}{change\hspace{0.1cm}in\hspace{0.1cm}x}$

slope-intercept b
b = y – mx

standard form of the equation of a line
ax + by + c = 0