a: \(3x^4-4x^3+1\)
\(=3x^4-3x^3-x^3+1\)
\(=3x^3\left(x-1\right)-\left(x-1\right)\left(x^2+x+1\right)\)
\(=\left(x-1\right)\left(3x^3-x^2-x-1\right)\)
b: \(x^3-19x-30\)
\(=x^3-4x-15x-30\)
\(=x\left(x-2\right)\left(x+2\right)-15\left(x+2\right)\)
\(=\left(x+2\right)\left(x^2-2x-15\right)\)
\(=\left(x+2\right)\cdot\left(x-5\right)\left(x+3\right)\)