3x + 1 = 7 + 2x
3x - 2x = 7 - 1
x = 6
=> D = { 6)
( 2x - 8) . ( 9 - 3x) = 0
\(\Rightarrow\hept{\begin{cases}2x-8=0\\9-3x=0\end{cases}\Rightarrow\hept{\begin{cases}2x=8\\3x=9\end{cases}\Rightarrow}\hept{\begin{cases}x=4\\x=3\end{cases}}}\)
=> C = { 3 ; 4}