Question

Tìm x:

a) (x+3)³-x(3x-1)²+(2x+1)(4x²-2x+1)-3x²=54

b) (x-3)³-(x-3)(x²+3x+9)+6(x+1)²+3x²=-33

Giúp mk lun nha!!

Answer 1

Tìm x:

a/ \(\left(x+3\right)^3-x\left(3x-1\right)^2+\left(2x+1\right)\left(4x^2-2x+1\right)-3x^2=54\)

<=> \(x^3+9x^2+27x+27-9x^3+6x^2-x+8x^3+1-3x^2-54=0\)<=> \(12x^2+26x-26=0\)

<=> \(\left[\begin{array}{} x=\dfrac{-13+\sqrt{481}}{12}\\ x=\dfrac{-13-\sqrt{481}}{12} \end{array} \right.\)

b/ \(\left(x-3\right)^3-\left(x-3\right)\left(x^2+3x+9\right)+6\left(x+1\right)^2+3x^2=-33\)

<=> \(x^3-9x^2+27x-27-x^3+27+6x^2+12x+6+3x^2+33=0\)

<=> 39x+39=0

<=> x=-1