they are negative inversees (they multily to get -1)
2
-1/2
use the square viewer (on TI)
The relationship between the slopes of two lines that are parallel is they are the same.
The relationship between the slopes of two lines that are perpendicular is they are negative inverses of each other (they multiply to -1). A line that is parallel to a line whose slope is 2 has slope 2. A line that is perpendicular to a line whose slope is 2 has slope -1/2.
What must be done to make the graphs of two perpendicular lines appear
to intersect at right angles when they are graphed using a graphing
utility?
The slopes of 2 lines that are parallel will be the same. the slopes of 2 lines that are perpendicular will have negative reciprocal slopes. parallel to a line with slope 2 is 2 (because parallel lines have the same slope). perpendicular to a line with slope 2 is -1/2 (the negative reciprocal...to find the negative reciprocal, just flip the slope of the original equation and change the sign)
and 
