Giải thích các bước giải:
\(\begin{array}{l}
{b^2} + 2bc - 4{a^2} + {c^2} = {b^2} + 2bc + {c^2} - 4{a^2}\\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {\left( {b + c} \right)^2} - {\left( {2a} \right)^2}\\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \left( {b + c + 2a} \right)\left( {b + c - 2a} \right)
\end{array}\)
