Lời giải:

1. 
$x^3+3x^2-16x-48=(x^3+3x^2)-(16x+48)=x^2(x+3)-16(x+3)$

$=(x+3)(x^2-16)=(x+3)(x-4)(x+4)$

2.

$4x(x-3y)+12y(3y-x)=4x(x-3y)-12y(x-3y)=(x-3y)(4x-12y)=4(x-3y)(x-3y)=4(x-3y)^2$

3.

$x^3+2x^2-2x-1=(x^3-x^2)+(3x^2-3x)+(x-1)=x^2(x-1)+3x(x-1)+(x-1)$

$=(x-1)(x^2+3x+1)$

\(\Leftrightarrow\left(x+1\right)^3=0\Leftrightarrow x+1=0\Leftrightarrow x=-1\)

<=>x³ +3x²1 +3x1²+1²=0

<=>(x+1)²=0

<=>x+1=0

<=>x=-1

a)=\(3x^3-15x^2+21x\)

b)\(=-2x^4y-10x^2y+2xy\)

c)\(=-x^3+6x^2+5x-4x^2+24x+20=-x^3+2x^2+29x+20\)

d)\(=2x^4-3x^3+4x^2-2x^2+3x-4=2x^4-3x^32x^2+3x-4\)

e)\(=x^2-4y^2\)

f)\(=-2x^2y^3+y-3\)

g)\(=3xy^4-\dfrac{1}{2}y^2+2x^2y\)

h)\(=9x^2-6x+1-7x^2-14=2x^2-6x-13\)

i)\(=x^2-x-3\)

j)\(=\left(x+2y\right)\left(x^2-2y+4y^2\right):\left(x+2y\right)=x^2-2y+4y^2\)

1a) \(=-\left(x^3-3x^2+3x-1\right)=-\left(x-1\right)^3\)

b) \(=-\left(x^3-3x^2+3x-1\right)=-\left(x-1\right)^3\)

\(a,=-\left(x-1\right)^3\left[=\left(1-x\right)^3\right]\\ b,=\left(1-x\right)^3\)

a. \(=-\left(x^3-3x^2+3x-1\right)=-\left(x-1\right)^3\)

b. \(=\left(1-x\right)^3\)

\(=\left(x-1\right)^3\)

(X-1)^3

\(x^3+3x^2+3x=-\dfrac{7}{8}\\ x^3+3x^2+3x+1=1-\dfrac{7}{8}\\ \left(x+1\right)^3=\dfrac{1}{8}\\ x+1=\dfrac{1}{2}\\ x=-\dfrac{1}{2}\)

Ta có: \(x^3+3x^2+3x=\dfrac{-7}{8}\)

\(\Leftrightarrow\left(x^3+3x^2+3x+1\right)=\dfrac{1}{8}\)

\(\Leftrightarrow\left(x+1\right)^3=\left(\dfrac{1}{2}\right)^3\)

\(\Leftrightarrow x+1=\dfrac{1}{2}\)

hay \(x=-\dfrac{1}{2}\)

Vậy: \(S=\left\{-\dfrac{1}{2}\right\}\)