To factor an expression, first you have to find the GCF or Greatest Common Factor of all of the pieces of the expression.
The GCF of 2y^2 and -4y is 2y
So, to factor this expression, we need to divide all of the pieces of the expression by the GCF.
2y(y-2)
2y^2 - 4y in completely factored form is 2y(y-2)
