two lines are perpendicular. if one has a slope of 1/21 what is the slope?

Question

 two lines are perpendicular. if one has a slope of 1/21 what is the slope?

Answer 1

The slope of a line perpendicular to another line has a slope that is the inverse reciprocal of the original line.  In this case we have the slope of one line at 1/21 so the inverse reciprocal is -21.