\(x-2y+x^2-4y^2\)
\(=\left(x-2y\right)+\left(x^2-4y^2\right)\)
\(=\left(x-2y\right)+\left(x-2y\right)\left(x+2y\right)\)
\(=\left(x-2y\right)\left(x+2y+1\right)\)
x - 2y + x² - 4y²
= (x - 2y) + (x² - 4y²)
= (x - 2y) + (x - 2y)(x + 2y)
= (x - 2y)(x + 2y + 1)