Factoring using the greatest common factor

Factor $$7\left(y-1\right)+x\left(y-1\right)$$

Factorize $$3xy-6y^2=3y\left(\ \ \ \ \ \ \ \ \ \right)$$

Factorize $$x^{\left(y+1\right)}-x^y$$

Factorize $$\frac{1}{2}x^y-2x^{\left(y-1\right)}$$

Factorize $$x^2y-5xy+9y$$

Factorize $$2x^y-4x^{\left(y-1\right)}+6x^{\left(y-2\right)}$$

Factorize $$2019^2+2019-2020^2$$

Factorize $$x\left(x-2\right)-x+2$$

Factorize $$x\left(x-y\right)+y\left(y-x\right)$$

Factorize $$15x\left(2x-y\right)^2+25\left(y-2x\right)^3$$