Question

1. Tìm x

a) (x+1)(x^{2 _} x+1) ^_ x ( x^_ 3 ) (x+1)= ^_27

b) ( x+3)(x² -3x+9)-x(x-1)(x+1)=14

c) 3(x-1)² - 3x(x -5) =1

Answer 1

b) \(\left(x+3\right)\left(x^2-3x+9\right)-x\left(x-1\right)\left(x+1\right)=14\)

\(\Rightarrow x^3+3^3-x\left(x^2-1^2\right)=14\)

\(\Rightarrow x^3+27-x^3+x=14\)

\(\Rightarrow27+x=14\)

\(\Rightarrow x=14-27=-13\)

c) \(3\left(x-1\right)^2-3x\left(x-5\right)=1\)

\(\Rightarrow3.\left(x^2-2x+1\right)-3x^2+15x=1\)

\(\Rightarrow3x^2-6x+3-3x^2+15x=1\)

\(\Rightarrow9x+3=1\)

\(\Rightarrow9x=1-3=-2\)

\(\Rightarrow x=-\frac{2}{9}\)