# Increase or Decrease

 A line with a positive slope points up to the right. A line with a negative slope points down to the right. A linear function is increasing when the $$x$$-values increase and the $$y$$-values increase. Created using Desmos.com This line is increasing. An increasing line has a positive slope $$(m>0)$$. A linear function is decreasing when the $$x$$-values increase and the $$y$$-values decrease. Created using Desmos.com This line is decreasing. A decreasing line has a negative slope $$(m<0)$$. A linear function is constant when the $$x$$-values increase and the $$y$$-values remain the same. This line is a horizontal line. A horizontal line has zero slope $$(m=0)$$. A linear function is undefined if the $$x$$-values are constant as the $$y$$-values vary. This line is a vertical line. A vertical line has undefined slope.