\(3x^3+2x^2-5=0\)
\(\Leftrightarrow3x^3-3x^2+5x^2-5=0\)
\(\Leftrightarrow3x^2\left(x-1\right)+5\left(x^2-1\right)=0\)
\(\Leftrightarrow3x^2\left(x-1\right)+5\left(x-1\right)\left(x+1\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(3x^2+5x+5\right)=0\)
\(\Leftrightarrow x-1=0\) ( vì \(3x^2+5x+5>0\) )
\(\Leftrightarrow x=1\)
Vậy .........................
\(x^3+3x^2+3x+1=0\)
\(\Leftrightarrow\left(x+1\right)^3=0\)
\(\Leftrightarrow x+1=0\)
\(\Leftrightarrow x=-1\)
Vậy........................
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