Gravitational Field?

Question

Three objects of equal mass (m) each are located on a corner of a square length L
What is the gravitational field on the fourth corner with no mass due to theses objects?


m1---------------m2
|..........................|
|..........................|
|..........................|
X-------------------m3

{<-------L------->}

Answer 1

g(m1) = g(m3) = Gm/L^2
g(m1+m3) = sqrt(2)*Gm/L^2
g(m2) = Gm/((sqrt(2)*L)^2 = 2Gm/L^2
g(total) = (2+sqrt(2))*Gm/L^2