\(25x^2-10x+1-y^2\)
\(=\left(5x-1\right)^2-y^2\)
\(=\left(5x-y-1\right)\left(5x+y-1\right)\)
\(4y^2-4x^2-4y+1\)
\(=\left(2y-1\right)^2-\left(2x\right)^2\)
\(=\left(2y+2x-1\right)\left(2y-2x-1\right)\)
\(-y^2+6y-9+x^2\)
\(=x^2-\left(y-3\right)^2\)
\(=\left(x+y-3\right)\left(x-y+3\right)\)