Bài giải
\(\left(x+3\right)\left(x^2-3x+9\right)-x\left(x-2\right)\left(x+2\right)=15\)
\(x^3-3x^2+9x+3x^2-9x+27-x\left(x^2-2^2\right)=15\)
\(x^3+27-x^3+2^2x=15\)
\(27-4x=15\)
\(4x=12\)
\(x=3\)
( x + 3 )( x2 - 3x + 9 ) - x( x - 2 )( x + 2 ) = 15
<=> x3 + 27 - x( x2 - 4 ) = 15
<=> x3 + 27 - x3 + 4x = 15
<=> 4x + 27 = 15
<=> 4x = -12
<=> x = -3
\(\left(x+3\right)\left(x^2-3x+9\right)-x\left(x-2\right)\left(x+2\right)=15\)
\(\Leftrightarrow x^3-3x^2+9x+3x^2-9x+27-x^3-2x^2+2x^2+4x=15\)
\(\Leftrightarrow4x+27=15\Leftrightarrow4x=-12\Leftrightarrow x=-3\)
