### Theory:

Definition of degree if the magnifier is a negative integer
A fraction with a whole negative multiplier is taken to be a fraction with a numerator of $$1$$, but the denominator is the same base with the opposite positive multiplier.
Example:
${a}^{-n}=\frac{1}{{a}^{n}}\phantom{\rule{0.147em}{0ex}}\left(n-\mathit{natural}\phantom{\rule{0.147em}{0ex}}\mathit{numbers}\right)$
Exceptions are the degree of $$0$$ with a negative multiplier, ${0}^{-3}$ and ${0}^{-1}$.
${3}^{-2}=\frac{1}{{3}^{2}}=\frac{1}{9}$

${10}^{-1}=\frac{1}{{10}^{1}}=\frac{1}{10}=0.1$

${\left(-4\right)}^{-3}=\frac{1}{{\left(-4\right)}^{3}}=\frac{1}{-64}=-\frac{1}{64}$

${\left(-1\right)}^{-3}=\frac{1}{{\left(-1\right)}^{3}}=\frac{1}{-1}=-1$
Important!
When increasing the share to a negative degree, the law shall be used:  ${\left(\frac{a}{b}\right)}^{-n}={\left(\frac{b}{a}\right)}^{n}$
${\left(\frac{2}{3}\right)}^{-3}={\left(\frac{3}{2}\right)}^{3}=\frac{27}{8}=3\frac{3}{8}$

Reference:
Mathematics Handbook for Students / J. Mencis, A. Sika - Riga: The Star, pp. 96 - 98, 1990