\(x^3-x^2-4x^2+8x^4\)
\(=x^3-5x^2+8x^4=x^2\left(x-5+8x^2\right)\)
\(-x^2-2x+15=-\left(x^2+2x+1-16\right)\)
\(=-\left[\left(x-1\right)^2-16\right]=-\left(x-5\right)\left(x+3\right)\)
\(3x^2+4x+1=4x^2+4x+1-x^2\)
\(=\left(2x+1\right)^2-x^2=\left(x+1\right)\left(3x+1\right)\)
3x2+4x+1
= (2x)2+ 4x+1-x
= ( 2x+1) - x