The line in this exampleis verticaland we foundthat the numericalvalueof the slopeisundefined.
In review, if you scana graphof a line from left to right,then,
- Lineswithpositiveslopespointup to the right,
- Lineswithnegativeslopespointdownto the right,
- Horizontallines havea slopeofzero, and
- Verticallineshaveundefinedslope.You can use thesegeneralrulesto checkyour workwhenworking
with slopesand lines.
Slopesof ParallelLines
Now that you knowhow to find the slopeof lines usingcoordinates,you can thinkabouthow lines and their
slopesare related.
Slopeof ParallelLinesTheoremIf two linesin the coordinateplaneare parallelthey
will havethe sameslope,conversely, if two lines in the coordinateplanehavethe same
slope,thoselines are parallel.Notethe proofof this theoremwill haveto wait until you havemoremathematicaltools,but for now you can
use it to solveproblems.
Example 5
Whichof the followingcouldrepresentthe slopeof a line parallelto the one following?