Объяснение:

6.

[tex](\frac{9a^{-2}}{7b^{-1}})^{-2} *\frac{3}{49}*a^{-2}b=(\frac{9}{7} )^{-2}*(\frac{a^{-2}}{b^{-1}})^{-2}* \frac{3}{49}*\frac{b}{a^2}=(\frac{7}{9} )^2*\frac{a^4}{b^2} *\frac{3b}{49a^2}=\frac{49*a^4*3b}{81*b^2*49a^2}=\frac{a^2}{27b}.[/tex]

7.

[tex]\frac{x^{-2}+x^{-5}}{x^{-6}+x^{-3}}= \frac{x^{-2}+x^{-5}}{x^{-3}+x^{-6}}= \frac{x^{-2}*(1+x^{-5-(-2)})}{x^{-3}*(1+x^{-6-(-3)})}}=\frac{1+x^{-3}}{x^{-1}*(1+x^{-3})} =\frac{1}{x^{-1}}=x.[/tex]