why (x-y)*(x+y)=2x

It doesn't:

(x-y)(x+y)       Use distributive property

x^2 + xy  - xy - y^2

=x^2 - y^2

i want to factorize this : (a-3b)(x+y)-(x-y)(3b-a) so my solution is (a-3b)(x+y)(x-y)

but the book gives this solution : 2x(a-3b)

is it a misprint or i am wrong?

ok i found my mistake .. thank you!!