\renewcommand{\labelenumii}{\arabic{enumii}.}
\begin{enumerate}
  \item \[ 100^{-\frac{1}{2}} = \frac{1}{100^\frac{1}{2}} = \frac{1}{\sqrt{100}} = \frac{1}{10} \]
  \item \[2^{log_2\left(2020\right)} = 2020\]
  \item \[ sin(-2020\pi) \rightarrow -2020 \bmod 1 = 0 \Leftrightarrow sin(-2020\pi) = 0\]
  \item \[\sqrt{y^2} = \pm y \]
  \item \[\left(\sqrt{y}\right)^2 = \left(y^{\frac{1}{2}}\right)^2 = y^\frac{1}{2} \cdot y^\frac{1}{2} = y^\frac{2}{2} = \sqrt{y^2} = \pm y \]
\end{enumerate}