Two bodies of masses m and M are placed a distance d apart. The gravitational potential at the position where the gravitational field due to them is zero is V, then : 

V = -G/d (m +M)

If P is the point of zero intensity, then :

\(x = \frac{\sqrt{M}}{\sqrt{M} + \sqrt{m}}.d \text{ and }\)

\(d - x = d - \frac{\sqrt{M}}{\sqrt{M} + \sqrt{m}}.d \text{ and }\)

Now potential at point P,

\(V = V_1 + V_2\)

\(V = -\frac{GM}{x} - \frac{GM}{d-x}\)

\(V = - \frac{G}{d} (\sqrt{m} + \sqrt{M})^2\)