a) x⁻⁵•x¹⁷ = x⁻⁵⁺¹⁷ = x¹²
б) x⁻³: x⁻⁹ = x⁻³⁻⁽⁻⁹⁾ = x⁻³⁺⁹ = x⁶
в) (x¹²y⁻⁸z²)⁻³ = x¹²*⁽⁻³⁾y⁻⁸*⁽⁻³⁾z²*⁽⁻³⁾ = x⁻³⁶y²⁴z⁻⁶
г) $$\left(\frac{x^{-3}}{y^{7}}\right)^{-5} \cdot \left(\frac{x^{4}}{y^{-7}}\right)^{-8} = \frac{x^{(-3)*(-5)}}{y^{7*(-5)}} \cdot \frac{x^{4*(-8)}}{y^{(-7)*(-8)}} = \frac{x^{15}}{y^{-35}} \cdot \frac{x^{-32}}{y^{56}} = x^{15-32} \cdot y^{35-56} = x^{-17}y^{-21}$$.