Straight-line equations are those that are first degree in both x and y.
Slope: the measure of steepness of a line. Two points on the line are needed to determine the slope.
where (x1, y1) and (x2, y2) are the coordinates of any two points on the line
* Equations must be in the slope-intercept form (solved for y ) in order to easily see what the slope and y -intercept are.
Parallel Lines have the same slopes and different y-intercepts
Perpendicular Lines have slopes that are negative reciprocals. If the slope of one line is 4 , then the slope of the perpendicular line is .
Graphing Linear Equations:
Vertical Lines are missing the y variable. The slope of a vertical line is undefined. x = 3 is the equation of a vertical line, where the x coordinate is always 3, and the y coordinate can be any value.
Horizontal Lines are missing the x variable. The slope of a horizontal line is zero. y = 2 is the equation of a horizontal line, where the y coordinate is always 2, and the x coordinate can be any value.
Horizontal and Vertical lines are perpendicular.