Undefined slope is when a line is exactly on the y-axis, for reasons unknown, the slope of a line on the y-axis cannot be determined, so therefore it it "undefined." A line with no slope is a line...
Undefined slopes are unnamed, if you go far enough into the problem your teacher will tell you how to figure them out You can also plot them on an intersecting number line.
Perpendicular lines = Right Angles, thus any right angle related things work, and you know the angle of one of the 3 (90 degrees) so the perpendicular line as a slope of 90 minus the the angle of the...