First, you take the x coordinate of C and subtract it from the x coordinate of B. 5-2=3. You then take the 3 and subtract it from the x value of point B which is 2 and 2-3=-1 which gives us the x coordinate of point A -1. then you take the Y coordinate of C and subtract it from the Y coordinate of B. 6-1=5. You then take the 5 and subtract it from the y value of point B which is 1 and 1-5=-4 which gives us the y coordinate of point A -5. And that gives you (-1,-4)
