( 3 . | x | - 2^4 ) . 7^3 = 2 . 7^4
⇔ 3 . | x | - 16 = 2 . 7^4 : 7^3
⇔ 3 . | x | - 16 = 2 . ( 7^4 : 7^3 )
⇔ 3 . | x | - 16 = 2 . 7
⇔ 3 . | x | - 16 = 14
⇔ 3 . | x | = 14 + 16
⇔ 3 . | x | = 30
⇔ | x | = 30 : 3
⇔ | x | = 10
⇔ \(\left[ \begin{array}{l}x = 10\\x = -10\end{array} \right.\)
Vậy , x ∈ { 10 ; - 10 }