\[\boxed{\mathbf{753\ (753).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[a_{1} = 3x + 4,\ \ a_{2} = 2x + 3,\]
\[\text{\ \ }a_{3} = x^{2},\ \ a_{4} = 2x^{2} + x\]
\[a_{1} + a_{4} = a_{3} + a_{2}\]
\[3x + 4 + 2x^{2} + x = 2x + 3 + x^{2}\]
\[x^{2} + 2x + 1 = 0\]
\[(x + 1)^{2} = 0\]
\[x = - 1\]
\[При\ x = - 1:\ \]
\[a_{1} = - 3 + 4 = 1,\ \ \]
\[a_{2} = - 2 + 3 = 1,\ \ a_{3} = 1,\ \ \]
\[a_{4} = 2 \cdot 1 - 1 = 1\]
\[Ответ:x = - 1 \Longrightarrow \ a_{1} = 1,\]
\[\ a_{2} = 1,\ a_{3} = 1,\ a_{4} = 1.\]