SOLUTION: Find the equation of each line. Write the answer in standard form using only integers. The problem is: The line through the points (-1,-3) and (2, -1). Please help!

Algebra ->  Linear-equations -> SOLUTION: Find the equation of each line. Write the answer in standard form using only integers. The problem is: The line through the points (-1,-3) and (2, -1). Please help!      Log On


   

Question 4887: Find the equation of each line. Write the answer in standard form using only integers.
The problem is:
The line through the points (-1,-3) and (2, -1).
Please help!
Answer by longjonsilver(2297) About Me  (Show Source):
You can put this solution on YOUR website!
find the gradient, m:
m+=+%28y%5B2%5D+-+y%5B1%5D%29%2F%28x%5B2%5D+-+x%5B1%5D%29

m+=+%28%28-3%29-%28-1%29%29%2F%28%28-1%29-%282%29%29
m+=+%28-3%2B1%29%2F%28-1-2%29
m+=+%28-2%29%2F%28-3%29
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.