Very often students get asked to show whether 2 linear equations are parallel (or perpendicular – they meet at a 90° angle) to each other when drawn on a graph. In fact, the criteria for determining that 2 lines are parallel or perpendicular is quite simple.

2 lines are PARALLEL if the coefficients of the x variable ARE THE SAME.

2 lines are PERPENDICULAR if the coefficients of the x variable MULTIPLY TO -1

Note: The linear equations must be in the form y = mx + c that is the coefficient of the y-variable must be 1 before attempting to determine if the lines are parallel or perpendicular.

Watch this short video for examples.

Solving Complex Problems - Where do I start... (I)
How To Determine the Equation of a Straight Line