\(\Leftrightarrow\left(x-3\right)^3-\left(x-3\right)^3+9\left(x^2+1\right)=63\)
\(\Leftrightarrow9\left(x^2+1\right)=63\)
\(\Leftrightarrow x^2+1=7\)
\(\Leftrightarrow x^2=6\)
\(\Leftrightarrow x=\pm\sqrt{6}\)
ta có: ( x –3 )³ – ( x – 3) . ( x² + 3x + 9) + 9 (x² + 1 ) = 63
\(\Leftrightarrow x^3-3.x^2.3+3.x.3^2-3^3+3.\left(x^2+3x+9\right)-x\left(x^2+3x+9\right)+9x^2+\)\(9=63\)
\(\Leftrightarrow\left(x^3-x^3\right)-\left(9x^2-9x^2\right)+27x-\left(27-27\right)-\left(9x-9x\right)-\left(3x^2-3x^2\right)\)\(+9=63\)
\(\Leftrightarrow27x+9=63\)
\(\Leftrightarrow3x+1=7\)
\(\Leftrightarrow3x=6\)
\(\Leftrightarrow x=2\)
vậy: x=2
