Understanding the gradients of perpendicular lines.

Understanding why the gradient of a perpendicular line is the negative reciprocal of the gradient of the original line.
Rotate the line (use the slider) and the triangle which defines its gradient.[br]What happens to the 'rise' and the 'run' as the lines become perpendicular?[br]What happens to the sign (positive or negative) of the gradient of the original line?
– Lesley Cowey

Information: Understanding the gradients of perpendicular lines.