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