\(=\left(2x+1\right)^2-y^2=\left(2x+y+1\right)\left(2x-y+1\right)\)
\(4x^2-y^2+4x+1=\left(4x^2+4x+1\right)-y^2\)
\(=\left(2x+1\right)^2-y^2=\left(2x+1-y\right)\left(2x+1+y\right)\)
\(4x^2-y^2+4x+1=\left(4x^2+4x+1\right)-y^2\)
\(=\left(2x+1\right)^2-y^2=\left(2x+1-y\right)\left(2x+1+y\right)\)