If two lines are perpendicular, how are their slopes related?

The slopes will be opposite reciprocals.

This means that they will be the opposite sign and the reciprocal.

For example, if the slopes of 2 eqautions are 3 and - 1/3, they are perpendicular.

If two lines are perpendicular and neither one is vertical, then one of the lines has a positive slope, and the other has a negative slope ... Theorem 105: If two nonvertical lines are perpendicular, then their slopes are opposite reciprocals of one another, or the product of their slopes is - 1.