It's all quite simple really.
\(ab^{-1} = \dfrac{a}{b^{1}} = \dfrac{a}{b}\)
\(ab^{-2} = \dfrac{a}{b^{2}}\)
\(ab^{-3} = \dfrac{a}{b^{3}}\)
\(and\,\,so\,\,on\)
\(and\)
\(ab^{1} = ab = \dfrac{a}{b^{-1}} = \dfrac{a}{b}\)
\(ab^{2} = \dfrac{a}{b^{-2}}\)
\(ab^{3} = \dfrac{a}{b^{-3}}\)
\(and\,\,so\,\,on\)
