![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/step1.JPG\")
\
Slope of the two points, ![\"\"](\"http://www.mathskey.com/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=3113839441e3480450ece8dbc4b861da.png\")
.
Replace ![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=2c2419605568ab3b290200ba53f4bf30.png\")
in slope formula.
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=d0ab953fa671d761f36fd02ab967f64d.png\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=59e871565a493324e9f9059ec8027040.png\")
(Subtract:![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=e0a2cf638f998167d818258c0c76281c.png\")
)
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=8eb075cadd4839e46748fff13a7d4cf9.png\")
(Subtract: ![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=0068a5adc8aa37bc80900c5b748ab3aa.png\")
)
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=7a933f78bb3d427e6fb0531c2ce016a1.png\")
or undefined![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/solution.JPG\")
The slope ![\"\"](\"http://www.mathskey.com/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=7a933f78bb3d427e6fb0531c2ce016a1.png\")
or undefined,So the line is vertical. \ \
\
Slope of the two points, .
Replace in slope formula.
(Subtract:)
(Subtract: )
or undefined
The slope or undefined,So the line is vertical. \ \