Question

Bài 14: Tìm x, biêt:

\(4)27x^2\left(x+1\right)-\left(3x+1\right)^3=-8\)

Answer 1

\(27x^2\left(x+1\right)-\left(3x+1\right)^3=-8\)

\(\Rightarrow27x^3+27x^2-27x^3-27x^2-9x-1=-8\)

\(\Rightarrow-9x-1=-8\)

\(\Rightarrow-9x=-7\)

\(\Rightarrow x=\frac{7}{9}\)

Answer 2

\(27x^2\left(x+1\right)-\left(3x+1\right)^3\)

\(27x^3+27^2-27x^3-27x^2-9x-1=-8\)

\(-9x-1=-8\)

\(-9x=-7\)

\(x=\frac{7}{9}\)

Answer 3

27x^2(x+1)-(3x+1)^3=-8

=>27x^3+27x^2-(27x^3+27x^2+9x+1)=-8

=>27x^3+27x^2-27x^3-27x^2-9x-1=-8

=>-9x=-7 =>x=7/9

      vậy x = 7/9

Answer 4

cac bạn co thể giải chỗ \(-\left(3x+1\right)^3\)cho mình hiểu đc không