Mathematics for IGCSE & O level - Coordinate Geometry (Section 1 - No. 36)
If a line has a gradient of -1/3, what is the gradient of a line perpendicular to it?
1/3
-3
3
-1/3
Explication
The gradient of a perpendicular line is the negative reciprocal of the original gradient. The negative reciprocal of -1/3 is 3.