a) $3x + 12 = 0$
$⇔ 3x = 12$
$⇔ x = 4$
b) $5 + 2x = x - 5$
$⇔ 2x - x = -5 - 5$
$⇔ x = -10$
c) $2x(x-2) + 5(x-2)=0$
$⇔ (2x+5)(x-2)=0$
$⇔ 2x +5 =0 ⇔ x = \frac{-5}{2}$
hoặc $x - 2 =0 ⇔ x = 2$
d) $\frac{3x-4}{2} = \frac{4x+1}{3}$
$⇔3(3x-4)=2(4x+1)$
$⇔9x - 12=8x + 2$
$⇔x=14$
e)$\frac{2x}{x-1} - \frac{x}{x+1}=1$ ĐKXĐ: $x$ khác $±1$
$⇔ \frac{2x(x+1)-x(x-1)}{(x-1)(x+1)}=1$
$⇔ 2x^2 +2x-x^2-x= x^2 -1$
$⇔ x^2+x = x^2-1$
$⇔x=-1$
