Honors Geometry Section 3.8 Lines in the Coordinate Plane
The slope of a line is a ratio that indicates how a line rises or falls from left to right.
The slope of a nonvertical line that contains the points is equal to the ratio
When graphing, it is helpful to think of slope as rise over run.
What would the slope of a vertical line be? Why?
Examples: Find the slope of the line through the given points.
Two nonvertical lines are parallel iff their slopes are equal. Note: Vertical lines will be parallel.
Two nonvertical lines are perpendicular iff their slopes are opposite reciprocals. Note: A horizontal line and a vertical line are perpendicular. change the sign flip the fraction
There are two forms for an equation of a line with which you should be familiar. Slope-intercept form: Point-slope form:
Example: Write an equation in point-slope form for the line through the point (3, -5) with a slope of.
Example: Write an equation, in slope- intercept form, for the line through the point (12, 5) that will be perpendicular to the line.
Example: Write an equation, in slope- intercept form, for the line through the points (2, -5) and (4, 2).