1: \(x^2+x-6\)
\(=x^2+3x-2x-6\)
=x(x+3)-2(x+3)
=(x+3)(x-2)
2: \(x^2-3x+2=x^2-x-2x+2=x\left(x-1\right)-2\left(x-1\right)\)
=(x-1)(x-2)
3: \(x^2+5x+4=x^2+x+4x+4\)
=x(x+1)+4(x+1)
=(x+1)(x+4)
4: \(x^4+4=x^4+4x^2+4-4x^2\)
\(=\left(x^2+2\right)^2-\left(2x\right)^2\)
\(=\left(x^2-2x+2\right)\left(x^2+2x+2\right)\)