Aljabar Bentuk 2

\begin{equation*}
\begin{split}
-49 + 14x - x^2& = -(49 - 14x + x^2)\\\\
-49 + 14x - x^2& = -(7^2 - 2\cdot 7 \cdot x + x^2)\\\\
-49 + 14x - x^2& = -(7 - x)^2\\\\
\end{split}
\end{equation*}