[tex] m = \dfrac{y_2 - y_1}{x_2 - x_1} = \dfrac{-1 - 2}{1 - 2} = \dfrac{-3}{-1} = 3 [/tex]
3 is a positive number, so the slope is positive.
Answer: D. positive
Positive slope: line goes up to the right.
Negative slope: line goes down to the right.
Zero slope: horizontal line.
undefined slope: vertical line.