Tính:

Bài 9:
1, (a - a^2+b^2/a+b)(1/b + 2/a-b)
2, 2/ab : (1/a - 1/b)^2 - a^2+b^2/(a-b)^2
3, (a-b)^2 + 4ab/a+b - a^2b + ab^2/ab
4,a-b/ab+b^2 + 3a+b/a^2 - ab . a-b/a+b
5, (m - m^2+n^2/m+n)(1/n + 2/m-n)