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Parallel and Perpendicular Lines
Parallel lines have the same slope. Think about what parallel lines look like: they are always the same
distance apart, so they must have the same amount of steepness.
Example
y = 3x + 7 and y = 3x + 12 are parallel.
The slopes of perpendicular lines are related, but it is a little more complicated. The slopes of
perpendicular lines are negative reciprocals of each other. If a line has a slope of , then the line
perpendicular to it has a slope of .
Example
are perpendicular.
Graphing Lines from Equations
Graphing a line from an equation is a quick task. You can graph a line without having to use several input
values, now that you know about the y-intercept and slope in each equation.
Follow these steps to graph a line from its equation:
1 Mark the y-intercept on the y-axis.
2 Starting from the y-intercept, count out the slope. (Remember, the run is the
denominator and the rise is the numerator. Pay attention to any negative signs!)
3 Make a mark at the point you reached after counting out the slope.
4 Connect the two points with a line.
Example
Graph
