i had some doubt's indirectly related to fermat's last theorem,

1)if i have

http://s13.postimage.org/owk66nz5j/image.png
and considering x,y constant(integers), n≥3 and integer,z a function of n, can i differentiate above relation wrt n?

2)if i have two relations with x,y constants and integers,n≥3

http://s13.postimage.org/owk66nz5j/image.png
http://s13.postimage.org/56xagh1v7/image.png
Can i find a and b? Would a and b be nth root of unity?