Question

What is the slope of this line?

Answer 1

The slope of this line is -2. 

rise/run

rise = 4 
run = -2 
  
      4 
   ------- = -2
     -2 

Using the points (1,0) & (0,2)

     2 - 0         2
  ----------- = ----- = -2
    0 - 1         -1

Answer 2

Since this line is descending, its slope should be negative:
Moreover the slope is nothing than the tangent of the angle formed with x-axis.
& the tangent of Ф = adjacent side/ opposite side).
If read well the graph you see that tan Ф = (4 units)/( - 8 units) = -4/8 = -1/2
Hence the slope = tan = -1/2