If the the line goes from quadrant 2 to quadrant 4 then the slope would be negative
to find the slope you take
Δy÷Δx .... this just means the change in y over the change in x
for example
if i had points A (-2,3) B( 4,-5)
I take the y points and subtract them from one another
and i then take the x coordinates and subtract them, take the end result and divide y over x
3-(-5) / -2-4
8/-6
4/-3
And since the final slope is negative therefore the line is going downwards and is negative