What does "z2" mean? If you mean , then you have described an impossible situation because . If you mean , then is utterly extraneous information because does not appear in the expression you want to simplify.
Furthermore, it is unclear whether you want to simplify or . You need to use parentheses more liberally.
Please read Formatting Math as Text before you post here again. Be sure to read all four pages.
John
My calculator said it, I believe it, that settles it