[tex]\dfrac{x^{-9}y^3}{x^{-7}y^8}=x^{-9-(-7)}y^{3-8}=x^{-2}y^{-5}=\dfrac{1}{x^2y^5}\\\\Used:\\\\\dfrac{a^n}{a^m}=a^{n-m}\\\\a^{-n}=\dfrac{1}{a^n}[/tex]
