The expression for gravity:
g=−G.1(−a(x+ro)+a0)2=−Ga21(x+aro−aoa)2=−Ga21(x+re)2
can be further simplified, it is basically g=1x2 scaled by −G along g axis, scaled along x axis by factor a and translated along x axis by a0 and since g=1x2 is symmetrical about x=0, we have
g=−G0.1(x+re)2
which is a more familiar form of the expression.