Đáp án:
\(\left[ \begin{array}{l}
A = - 2071\\
A = - 1961
\end{array} \right.\)
Giải thích các bước giải:
Có:
\(\begin{array}{l}
7a = 5b\\
\to a = \frac{5}{7}b\\
Thay:a = \frac{5}{7}b\\
\to \left( {\frac{5}{7}b} \right).b = 875\\
\to \frac{5}{7}{b^2} = 875\\
\to {b^2} = 875:\frac{5}{7} = 1225\\
\to \left[ \begin{array}{l}
b = \sqrt {1225} \\
b = - \sqrt {1225}
\end{array} \right.\\
\to \left[ \begin{array}{l}
b = 35\\
b = - 35
\end{array} \right. \to \left[ \begin{array}{l}
a = \frac{5}{7}.35\\
a = \frac{5}{7}.\left( { - 35} \right)
\end{array} \right.\\
\to \left[ \begin{array}{l}
a = 25\\
b = - 25
\end{array} \right.\\
A = 2a - 3b - 2016\\
\to \left[ \begin{array}{l}
A = 2.25 - 3.35 - 2016\\
A = 2.\left( { - 25} \right) - 3.\left( { - 35} \right) - 2016
\end{array} \right.\\
\to \left[ \begin{array}{l}
A = - 2071\\
A = - 1961
\end{array} \right.
\end{array}\)
