8. 1/x-1 + 2/x+! = x/x^2 - 1

1x−1+2x+1=xx2−1 (ĐKXĐ: x≠±1)

⇔x+1+2x−1x−1x+1=xx2−1⇔3x−1x−1x+1=xx−1x+1⇒3x−1=x⇔2x=1⇔x=12  TM

S=12