Electric charges at the corners of a square

[Karol]

Homework Statement

3 point charges, q₁=+2E-9[Coulomb] are placed at the corners of a square of 0.2[m] edge. what is the potential at the center.

Homework Equations

The potential of a point charge at distance r: $$V[Volt]=K\frac{q}{r}$$
$K=\frac{1}{4\pi\varepsilon_0}=9\times 10^9$

The Attempt at a Solution

The distance from the center to each of the corners: $$r=\frac{0.1}{\cos 45^0}=0.1414[m]$$
$V_b=9\times 10^9\frac{2\times 10^{-9}}{0.1414}\cdot 3=382[Volt]$
I am not sure but it should be 254[V]

 

[ehild]

254 would be the potential in case of two charges, or four 1E-9 C charges at each corner. The given answer must be wrong.

 

[Karol]

Thanks, Ehild