Section+1.4


 * Section 1.4 ** includes slope, horizontal and vertical lines, point-slope form, slope-intercept form and general form as well as parallel and perpendicular lines.

for two points A (x1, y1) and B (x2, y2). Another way of thinking about slope is m = (average x, average y)
 * Slope Formula** - slope is represented by a lower case m. Often slope is referred to as rise/run. The formula is


 * Parallel Lines** - two lines are parallel if and only if they have identical slopes. The slopes are represented as m1 and m2. If the slope of one line is 3/4, then a parallel line will also have a slope = 3/4.


 * Perpendicular Lines** - two lines are perpendicular if and only if they have slopes that are negative reciprocals, or opposite reciprocals. If the slope of a line is 2, then a perpendicular line must have a slope of -1/2.


 * Slope Intercept Form -** is y = mx + b, where m is the slope and b is the y-intercept (0,b). Slope intercept is probably the most often used form of a line.

Another form of point slope form is f(x) = m(x - x1) + y1. This is helpful because it can be plugged straight into the calculator.
 * Point Slope Form -** is easliy used when the slope and a point on the line are given.


 * General Form** - is Ax + By + C = 0, where A and B are not both zero. This is an additional form of a line but is not as useful as point slope or slope intercept forms. All equations with x and y both to the first power are linear equations.

Examples include: y = 6 or y = -843
 * Horizontal Lines** - A horizontal line has a slope of 0. The equation is written as y = b, where is b is a constant.

Examples include: x = 4 or x = -15.6
 * Vertical Lines** - A vertical line has an undefined slope. The equation is written as x = a, where a is a constant.