(2a+2)(2a+4)-2a(2a+2)=129

Đáp án:

Giải thích các bước giải:

\[\begin{array}{l}\left( {2a + 2} \right)\left( {2a + 4} \right) – 2a\left( {2a + 2} \right) = 129\\ \Leftrightarrow \left( {2a + 2} \right)\left( {2a + 4 – 2a} \right) = 129\\ \Leftrightarrow \left( {2a + 2} \right).4 = 129\\ \Leftrightarrow 2.\left( {a + 1} \right).4 = 129\\ \Leftrightarrow 8.\left( {a + 1} \right) = 129\\ \Leftrightarrow a + 1 = \frac{{129}}{8}\\ \Rightarrow a\,\,\,\,\,\,\,\,\, = \frac{{129}}{8} – 1\\ \Rightarrow a\,\,\,\,\,\,\,\,\, = \frac{{121}}{8}\end{array}\]