Question

8(x-3)³ + x³ = 6x² - 12x +8

Answer 1

\(8.\left(x-3\right)^3+x^3=6x^2-12x+8\)

\(\Leftrightarrow\left(2x-6\right)^3=-x^3+6x^2-12x+8\)

\(\Leftrightarrow\left(2x-6\right)^3=\left(2-x\right)^3\)

\(\Leftrightarrow2x-6=2-x\)

\(\Leftrightarrow3x=8\)

\(\Leftrightarrow x=\dfrac{8}{3}\)

Vậy pt có nghiệm x = \(\dfrac{8}{3}\)

Answer 2

\(8\left(x-3\right)^3+x^3=6x^2-12x+8\)

\(< =>8\left(x^3-9x^2+27x-27\right)+x^3-6x^2+12x-8=0\)

\(< =>8x^3-72x^2+216x-216+x^3-6x^2+12x-8=0\)

\(< =>9x^3-78x^2+228x-224=0\)

\(< =>\left(3x-8\right)\left(3x^2-18x+28\right)=0\)

đến đây dễ rồi bạn tự làm