Equations of lines
| Equation | Description |
| y = mx + b | Slope-intercept form: slope m , y-intercept b |
| y – y1 = m(x – x1) | Point-slope form: slope m , line passes through (x1 , y1) |
| x= k | Vertical line: x –intercept k, no y – intercept (except when k = 0), undefined slope |
| y = k | Horizontal line : y-intercept k, no x-intercept (except when k = 0 ), slope 0 |