Lời giải:
a)
\(3x^4+11x^3-7x^2-2x+1\)
\(=(3x^4-x^3)+12x^3-4x^2-3x^2+x-3x+1\)
\(=x^3(3x-1)+4x^2(3x-1)-x(3x-1)-(3x-1)\)
\(=(3x-1)(x^3+4x^2-x-1)\)
b)
\(x^4-6x^3+11x^2-6x+1\)
\(=(x^4-6x^3+9x^2)+2x^2-6x+1\)
\(=(x^2-3x)^2+(2x^2-6x)+1\)
\(=(x^2-3x)^2+2(x^2-3x)+1^2\)
\(=(x^2-3x+1)^2\)