\(x^4+6x^2y+9y^2-1=\left(x^2+3y\right)^2-1=\left(x^2+3y-1\right)\left(x^2+3y+1\right)\)
\(x^4+6x^2y+9y^2-1\)
\(=\left[\left(x^2\right)^2+2.x^2.3y+\left(3y\right)^2\right]-1^2\)
\(=\left(x^2+3y\right)^2-1^2\)
\(=\left(x^2+3y-1\right)\left(x^2+3y+1\right)\)
\(x^4+6x^2y+9y^2-1\)
\(=\left(x^2+3y\right)^2-1\)
\(=\left(x^2+3y+1\right)\left(x^2+3y-1\right)\)