\(2x^2-50x=2x.\left(x-25\right)\)
\(x^2-6x+9-4y^2\\ =\left(x-3\right)^2-\left(2y\right)^2\\ =\left(x-3-2y\right).\left(x-3+2y\right)\)
\(2x^2-50x=2x\left(x-50\right)\)
\(x^2-6x+9-4y^2=\left(x-3\right)^2-4y^2=\left(x+2y-3\right)\left(x-2y-3\right)\)