Bài 2:
a: \(=\left(x-y\right)\left(x+y\right)-5\left(x-y\right)=\left(x-y\right)\left(x+y-5\right)\)
b: \(=3\left(x^2-y^2-4x+4y\right)\)
\(=3\left[\left(x-y\right)\left(x+y\right)-4\left(x-y\right)\right]\)
\(=3\left(x-y\right)\left(x+y-4\right)\)
c: =(x-1)(x-2)