Question

Tìm x, biết : (x-3)^2 - (x-3)(x^2 +3x + 9)+9(x+1)^2 = 15

Answer 1

Sửa đề: \(\left(x-3\right)^3-\left(x-3\right)\left(x^2+3x+9\right)+9\left(x+1\right)^2=15\)

=>\(x^3-9x^2+27x-27-\left(x^3-27\right)+9\left(x^2+2x+1\right)=15\)

=>\(x^3-9x^2+27x-27-x^3+27+9x^2+18x+9=15\)

=>\(45x+9=15\)

=>45x=6

=>\(x=\dfrac{6}{45}=\dfrac{2}{15}\)