a: \(\Leftrightarrow5x\left(x^2-6x+9\right)-5\left(x^3-3x^2+3x-1\right)+15x^2-60-5=0\)
\(\Leftrightarrow5x^3-30x^2+45x-5x^3+15x^2-15x+5+15x^2-65=0\)
\(\Leftrightarrow30x-60=0\)
hay x=2
b: \(\Leftrightarrow x^3+9x^2+27x+27-x\left(9x^2+6x+1\right)+8x^3+1-3x^2=42\)
\(\Leftrightarrow9x^3+6x^2+27x+28-9x^3-6x^2-x=42\)
=>26x=14
hay x=7/13