How can I factor a polynomial with 4 unlike terms?

[EricPowell]

3x-3y-x^2+y^2
My textbook says the answer is (3-x-y)(x-y)

I tried to factor it two different ways. One time I got
3(x-y)-x^2+y^2
And the other time I got
x(3-x)-y(3-y)

I've never seen a polynomial with 4 unlike terms like this before, and I am not understanding how 3-x-y is part of the answer (it has three terms in it). How does one go about factoring something like this?

 

[Curious3141]

3x-3y-x^2+y^2
My textbook says the answer is (3-x-y)(x-y)

I tried to factor it two different ways. One time I got
3(x-y)-x^2+y^2
And the other time I got
x(3-x)-y(3-y)

I've never seen a polynomial with 4 unlike terms like this before, and I am not understanding how 3-x-y is part of the answer (it has three terms in it). How does one go about factoring something like this?

Hint: 3x-3y = 3(x-y)

and

-x^2 + y^2 = -(x^2 - y^2) = -(x+y)(x-y)

EDIT: Nice April Fool's joke, Evo. I love that avatar. Think I'll keep her.