Finding the slope and rise over run

Find the slope of the line through the following pairs of points.
(1, -1) (4,0)

i did y2-y1 / x2-x1 to find the slope

and i got -1/3 for the slope but that isn't correct

can you please explain how to do this problem

thanks

You have to be very careful with negative signs. Do not try to make any short cuts, you will inevitably make a mistake such as you have done here. Always write it out in full.


(-1 - 0) . . . . (-1) . . . . .1
--------- . = . ------. = . ----
(1 - 4) . . . . .(-3) . . . . .3


Or, you could try it the other way around (It does not matter which point you call (x1, y1), and which (x2,y2), as long as you are consistent when applying the formula). You will get the same answer (or you ought to get the same answer if you do it correctly !)

(0 - (-1)) . . . . +1 . . . . . 1
----------- . = . ----- . = . ----
. (4 - 1) . . . . . .3 . . . . . .3

y2 = 0
y1 = -1

y2 - y1 = 0 - -1 = 0 + 1 = 1

x2 = 4
x1 = 1

x2 - x1 = 4 - 1 = 3

You had a negative sign missing somewhere.