Question 970281
Lines that are perpendicular to one another have slope products=-1

y=x has a slope of 1
Therefore, the other line perpendicular to it has slope (-1)  

Point slope formula

y-y1=(-1) (x-x1)  ; the -1 slope is visible.

use the point (2,2)

y-2= (-1) (x-2)

y-2= -x +2  ; (-1) (-2) =+2
add 2 to both sides

y=-x +4

{{{graph (300,200,-4,4,-4,4,x,-x+4)}}}    The lines don't look exactly perpendicular, because the tick marks are not the same length on both axes.