…. Question …. in progress 0 Môn Toán Mộc Miên 2 years 2021-04-22T09:46:36+00:00 2021-04-22T09:46:36+00:00 1 Answers 6 views 0
Answers ( )
Đáp án:
a=7
Giải thích các bước giải:
\(\begin{array}{l}
\left\{ \begin{array}{l}
2x – y = 5\\
x + y = 3a – 2
\end{array} \right.\\
\to \left\{ \begin{array}{l}
3x = 3a + 3\\
y = 2x – 5
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x = a + 1\\
y = 2\left( {a + 1} \right) – 5 = 2a – 3
\end{array} \right.\\
\dfrac{{{x^2} – y – 5}}{{y + 1}} = 4\\
\to \dfrac{{{a^2} + 2a + 1 – 2a + 3 – 5}}{{2a – 3 + 1}} = 4\\
\to \dfrac{{{a^2} – 1}}{{2a – 2}} = 4\\
\to \dfrac{{\left( {a – 1} \right)\left( {a + 1} \right)}}{{2\left( {a – 1} \right)}} = 4\left( {a \ne 1} \right)\\
\to \dfrac{{a + 1}}{2} = 4\\
\to a + 1 = 8\\
\to a = 7
\end{array}\)