a) F = 1/(2√x - 2) - 1/(2√x + 2) + √x/(1 - x)
= 1/2.(√x - 1) - 1/2.(√x + 1) - √x/(x - 1)
= [(√x + 1) - (√x - 1) - 2√x] /[2(√x + 1)(√x - 1)]
= (√x + 1 - √x + 1 - 2√x) /[2(√x + 1)(√x - 1)]
= (2√x + 2) /[2(√x + 1)(√x - 1)]
= 2(√x + 1) /[2(√x + 1)(√x - 1)]
= 1/(√x - 1)
b) F = -1/3 
<=> 1/(√x - 1) = -1/3
<=> √x - 1 = -3
<=> √x = -2 (vô lý)
<=> vô nghiệm