algebra
posted by caduceus .
Which choice could be the equation of a line perpendicular to the line represented by this equation?
y = 5
for this question, i put this:
y = 1/5x
but, it says i am wrong. how is that? 5 is 5/1, and so the negative reciprocal of 5/1 would be 1/5, right?

You are correct. Maybe they anticipated
(1/5)*x, or x/5, or 0.2x, or maybe they are just wrong. 
y = 5 or y = 0x + 5
is a horizontal line with slope of 0
Thus a perpendicular line would be a vertical line, which has an undefined slope.
Any vertical line has the form x = k , where k is a constant