slope = rise / run
m = (y2 - y1) / (x2 - x1)
m = (4 - -1) / (-3 - 2)
m = (4 +1) / (-3 -2)
m = 5/(-5)
m = -1
start with point slope form
y - y1 = m (x - x1)
pick one of the points (doesn't matter which one), we'll pick (2, -1)
y - -1 = -1 (x - 2)
y + 1 = -x + 2
y = -x + 1 (slope-intercept form)