A line is represented mathematically by a "linear" equation, which takes the following standard form:
y = mx + b
This equation defines the point y given the input x, and parameters m and b.
m is the slope. A downward sloping straight line will have a negative value of m. What this means is that as x increases in value, y decreases in value. Thus there is a negative correlation between the variables x and y. The parameter b establishes a fixed reference point, namely the point (0,b).
negative correlation between the two variables.