3: Ta có: \(\left(x+3\right)^3-\left(x+1\right)^3=56\)
\(\Leftrightarrow x^3+9x^2+27x+27-x^3-3x^2-3x-1-56=0\)
\(\Leftrightarrow6x^2+24x-30=0\)
\(\Leftrightarrow x^2+4x-5=0\)
\(\Leftrightarrow\left(x+5\right)\left(x-1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-5\\x=1\end{matrix}\right.\)
(x - 2)3 - x(x - 3)2 = 1
<=> x3 - 6x2 + 12x - 8 - x(x2 - 6x + 9) = 1
<=> x3 - 6x2 + 12x - 8 - x3 + 6x2 - 9x = 1
<=> x3 - x3 - 6x2 + 6x2 + 12x - 9x = 1 + 8
<=> 3x = 9
<=> x = 3