\(=\left(4x^2-4xy+y^2\right)-\left(25a^2-10a+1\right)=\left(2x-y\right)^2-\left(5a-1\right)^2\)
\(=\left(2x-y-5a+1\right)\left(2x-y+5a-1\right)\)
\(=\left(4x^2-4xy+y^2\right)-\left(25a^2-10a+1\right)\\ =\left(2x-y\right)^2-\left(5a-1\right)^2\\ =\left(2x-y-5a+1\right)\left(2x-y+5a-1\right)\)