$g$) $4.x^3 + 12 =120$
$⇔ 4.x^3 + 4.3 = 120$
$⇔ 4.(x^3 + 3) = 120$
$⇔ x^3 + 3 = 30$
$⇔ x^3 = 27$
$⇔ x^3 = 3^3$
$⇔ x=3$
Vậy $x=3$.
$h$) $3^2 - 2(x-1) = 5^5 : 5^4$
$⇔ 9 - 2(x-1) = 5$
$⇔ 2(x-1) = 4$
$⇔ x-1 = 2$
$⇔ x=3$
Vậy $x=3$.
$i$) $2^x = 2^2 . 2$
$⇔ 2^x = 2^3$
$⇔ x=3$
Vậy $x=3$.
$k$) $3 . 2^x - 3 = 45$
$⇔ 3.(2^x - 1) = 45$
$⇔ 2^x - 1 =15$
$⇔ 2^x = 16$
$⇔ 2^x = 2^4$
$⇔ x=4$
Vậy $x=4$.
$l$) $1500 : [(30x+40):x] = 30$
$⇔ (30x+40):x = 50$
$⇔ 50x = 30x + 40$
$⇔ 50x - 30x = 40$
$⇔ 20x = 40$
$⇔ x=2$
Vậy $x=2$.
$m$) $x^3 = x$
$⇔ x^3 - x = 0$
$⇔x.(x^2-1) = 0$
$⇒$ \(\left[ \begin{array}{l}x=0\\x=1\end{array} \right.\)
Vậy $x$ $∈$ `{0;1}`.
