y=mx+b where m is the slope and b is the y-intercept. You can find m by using the equation: (y2-y1)/(x2-x1). So for this problem: (-1-2)/(2-(-1))=-3/3 or -1. To find b you can just pick one of the two points and put into the equation and solve for b. For this problem using (-1,2): 2=-1*(-1)+b, 2=1+b, 1=b. So the equation of this line would be y=-x+1.