Giải thích các bước giải:
$a)(3x-1)^3+8=0$
$⇔(3x-1)^3=- 8$
$⇔3x-1=-2$
$⇔3x=-1$
$⇔x=-\dfrac{1}{3}$
$\text{Vậy $x=-\dfrac{1}{3}$}$
$b)(2x-3)^3+(6x-17)^3=0$
$⇔(2x-3)^3=-(6x-17)^3$
$⇔2x-3=-6x+17$
$⇔8x=20$
$⇔x=\dfrac{20}{8}=\dfrac{5}{2}$
$\text{Vậy $x=\dfrac{5}{2}$}$
$c)x^3-3x^2+3x-1=0$
$⇔(x-1)^3=0$
$⇔x-1=0$
$⇔x=1$
$\text{Vậy $x=1$}$
$d)7x^3-3x^2-3x-1=0$
$⇔7x^3-7x^2+4x^2-4x+x-1=0$
$⇔7x^2(x-1)+4x(x-1)+(x-1)=0$
$⇔(7x^2+4x+1)(x-1)=0$
$⇔$ \(\left[ \begin{array}{l}7x^2+4x+1=0\text{(Vô lý)}\\x-1=0\end{array} \right.\) $⇔$ \(\left[ \begin{array}{l}x∈∅\\x=1\end{array} \right.\)
$\text{Vậy $x=1$}$
Học tốt!!!
