Another Question about Electric Potential

[simplicity12]

Homework Statement

Three charges are placed at the corners of an equilateral triangle with sides of length 2.0 m. Determine the electric potential at the midpoint of each side of the triangle. The three charges at the corners of the triangle at +4.0 X 10^-6 C, +2.0 X 10^-6 C, and -4.0 10^-6 C.

Homework Equations

V=kq/r

The Attempt at a Solution

I tried finding the electric potential of each of the charges to the midpoint, meaning that the r=1.0 m, and then adding the electric potential on either side of the midpoint together... but it's not working...
For example:
For the midpoint betweeen the charges +4.0 X 10^-6 C and +2.0 X 10^-6 C, i found the electric potential from the midpoint to the charge +4.0 X 10^-6 C, in which i got 36000 V and then i found the electric potential from the midpoint to the charge of +2.0 X 10^-6 C, and i got 18000 V. I added these two values together... but i didn't get the right answer. The answers for the three midpoints of the triangle are 1.0 X 10^4 V, 3.3 X 10^4 and 2.8 X 10^3 V. Can someone please help?

 

[Mindscrape]

Did you use 1m for all your distances? What distance did you use for the charge opposite the midpoint?

 

[simplicity12]

oops! I didn't know before hand that I'm suppose to consider the charge across from the midpoint. Thank you for the hint :D

 

[arpeggio]

I am stuck in the same question
I tried to use V= kq/r but I don't know what is r for each point
the triangle are 2m length so at one of the midpoint it is \sqrt{3}, 1, 1, away from each charge

do you add v=kq/r1 + v=kq/r2 and so on?
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I got it!