Question

2x(x+2)^2-8x^2=2(x-2)(x^2+2x+4)

Answer 1

\(2x\left(x+2\right)^2-8x^2=2\left(x-2\right)\left(x^2+2x+4\right)\)

\(\Leftrightarrow2x^3+8x=2\left(x^3-8\right)\)

\(\Leftrightarrow2x^3+8x=2x^3-16\)

\(\Leftrightarrow2x^3+8x-2x^3=2x^3-16-2x^3\)

<=> 8x = -16

=> x = 2

Answer 2

2x(x+2)² -8x²=2(x-2)(x²+2x+4)

<=>2x(x²+4x+4)-8x²=(2x-4)(x²+2x+4)

<=>2x³+8x²+8x-8x²=2x³+4x²+8x-4x²-8x-16

<=>2x³+8x              = 2x³-16

<=>2x³+8x-2x³       = -16

<=>8x                     =-16

<=>x                       =-16/8

<=>x                      = -2

Vậy:         S={-2}.