What is the slope of the line between (3, - 4) and (-2, 1) ?

Slope formula : (y2 - y1) / (x2 - x1)

(3,-4) ... this is set 1, so x1 = 3 and y1 = - 4

(-2,1) ... this is set 2, so x2 = - 2 and y2 = 1

now we sub ... but pay close attention to the signs

slope = (1 - (-4) / (-2 - 3) = (1 + 4) / - 5 = 5/-5 = - 1 < = = slope