Visual Optical Illusion Test: An optical illusion is a mind-bending illustration of an object or drawing or picture that has different appearances if looked at from different perspectives. There are ...

Horizontal lines run left to right, parallel to the horizon, with slope 0 and equation y = k. Vertical lines run top to bottom, perpendicular to the horizon, with undefined slope and equation x = k.

Higher - The gradients of two perpendicular lines will always multiply to make –1. Make sure you are familiar with finding the equation of a line and calculating gradient to understand equations of ...