(x+2).(x2−4x+1)−(x3−2x2+2)=−18⇔x3−4x2+x+2x2−8x+2−x3+2x2−2=−18⇔−7x=−18⇔x=\(\dfrac{7}{18}\)

$\iff x^2+\frac{1}{3}x-\left(x^2-\frac{5}{2}x+8x-20\right)=\frac{1}{5}$

$\iff x^2+\frac{1}{3}x-x^2-\frac{11}{2}x+20=\frac{1}{5}$

=>-31/6x=-99/5

hay x=594/155

$(x+2)(x^2-2x+4)-x(x^2+5)=2$

$\iff x^3+8-x^3-5x=2$

$\iff -5x=-6$

$\iff x=\frac{6}{5}$

Vậy $S=\left\{\frac{6}{5}\right\}$

$\iff x^3+8-x^3-5x=2$

=>8-5x=2

=>5x=6

hay x=6/5

$\left(x+5\right)\left(x-5\right)x-\left(x+2\right)\left(x^2-2x+4\right)=3$

$\iff \left(x^2-25\right)x-\left(x^3+8\right)=3$

$\iff x^3-25x-x^3-8=3$

$\iff -25x=11$

$\iff x=-\frac{11}{25}$

Vậy $S=\left\{-\frac{11}{25}\right\}$