
\begin{enumerate}
\begin{multicols}{2}
\item $A=\numprint{897526}^2-\numprint{897525}\times\numprint{897527}$.

Posons $x=\numprint{897526}$. Alors,
\begin{align*}
A & = x^2 - (x-1)(x+1)\\
& = x^2 - (x^2 - 1^2)\\
& = x^2 - x^2 + 1\\
\Aboxed{A & = 1}
\end{align*}

\item $B=\numprint{100001}^2-\numprint{99999}^2$.

Posons $x=\numprint{100000}$. Alors,
\begin{align*}
B & = (x+1)^2-(x-1)^2\\
& = \big[(x+1)-(x-1)\big]\big[(x+1)+(x-1)\big]\\
& = 4x.
\end{align*}

Donc $\boxed{B=4\times\numprint{100000}=\numprint{400000}}$.
\end{multicols}
\end{enumerate}
