`(n - 1)` equal point masses each of mass `m` are placed at the vertices of a angular n-polygon. The vacant vertex has `a` position vector `a` with respect to the centre of the polygon. Find the position vector of centre of mass.

Explanation

Let us consider `vecr` as the position vector of the centre of mass C of a regular n-polygon. Also given, (n - 1) equal point masses, each of mass m, are placed at its (n-1) vertices with vacant vertex having a position vector `veca` with respect to the centre of the regular n-polygon.
So `((n-1) mr+ma)/(mxx n)=0`
or `(n-1) mr+ma=0`
or `r=-a//(n-)`