a) x - 1 / x + 1 / x + 1 = 2x - 1/x^2 + x
ĐKXĐ:x khác 0;-1
<=>(x - 1)(x + 1) / x(x + 1) + x / x(x+1) = 2x + 1 / x(x + 1)
=>(x - 1)(x + 1) + x = 2x + 1
<=>x^2 - 1^2 + x = 2x + 1
<=>x^2 + x - 2x - 1 - 1 = 0
<=>x^2 - x - 2 = 0
<=>x^2 + x - 2x - 2 = 0
<=>x(x + 1) - 2(x + 1) = 0
<=>(x - 2)(x + 1) = 0
<=>x - 2 = 0
x + 1 = 0
<=>x = 2(t/m)
x = -1(loại vì ĐKXĐ: x khác 0;-1)
Vậy S = {2}