BPT\(\Leftrightarrow\left(x-3\right)\left(x^2+3x+9\right)\left(x-1\right)\left(x^2+x+1\right)\left(3-x\right)\left(x+1\right)\ge0\)
\(\Leftrightarrow\left(x-3\right)\left(x-1\right)\left(3-x\right)\left(x+1\right)\ge0\) VÌ \(\left(\left(x^2+3x+9\right).\left(x^2+x+1\right)>0với\forall x\right)\)
\(\Leftrightarrow\left(x-3\right)^2.\left(1-x\right)\left(1+x\right)\ge0\)
\(\Leftrightarrow\left(1-x\right)\left(1+x\right)\ge0\left(vì\left(x-3\right)^2\ge0voi\forall x\right)\)
\(\Leftrightarrow-1\le x\le1\)