Given that,

Three charges are -q, q and q.

Side equilateral triangle = a

We know that,

For equilateral triangle ABC,

We know that,

Altitude of equilateral triangle is

We need to calculate the value of r

Using formula of r

Put the value of h

We need to calculate the net electric potential at centroid of the triangle​

Using formula of electric potential

Put the value into the formula  

Hence, The net electric potential at centroid of the triangle​ is