Question 4887
find the gradient, m:

{{{m = (y[2] - y[1])/(x[2] - x[1])}}}


{{{m = ((-3)-(-1))/((-1)-(2))}}}
{{{m = (-3+1)/(-1-2)}}}
{{{m = (-2)/(-3)}}}
m = 2/3


So, y=mx+c, we now have y=(2/3)x+c


Put in one of the coordinate pairs now, to find c - either, it doesn't matter. I will pick (2,-1).


-1 = (2/3)(2) + c
-1 = 4/3 + c
c = -1 - 4/3
c = -3/3 - 4/3
c = -7/3


so equation is y = (2/3)x - 7/3, but the Q wants everything in integers, not fractions, so...multiply all terms by 3 to give 3y = 2x - 7. Done!


To be safe, use the other coordinates that you did not use...put the x value into thet equation and see if you get y=-3 out. If you do, your equation is correct. If not, you have calcualted something wrong somewhere, so you can check your working.


jon.