Tìm số tự nhiên x, biết: (x – 12) . 45 = 2.48

(x – 12) . $4^{5}$  = 2 . $4^{8}$ 
$\Longrightarrow$ (x - 12) . $(2^{2})^5$ = 2 . $(2^{2})^8$ 
$\Longrightarrow$ x - 12 . $2^{10}$  = 2 . $2^{16}$ 
$\Longrightarrow$ x - 12 . $2^{10}$  = $2^{17}$ 
$\Longrightarrow$ x - 12 = $2^{17}$ : $2^{10}$ 
$\Longrightarrow$ x - 12 = $2^{7}$ 
$\Longrightarrow$ x - 12 = 128
$\Longrightarrow$ x = 128 + 12
$\Longrightarrow$ x = 140
Vậy x = 140