Đạo hàm của hàm số f(x) = (3^x - 1)/(3^x + 1) là. f'(x) = -2

A. $f\text{'}\left(x\right)=-\frac{2}{{\left(3^x+1\right)}^2}.3^x$

B. $f\text{'}\left(x\right)=\frac{2}{{\left(3^x+1\right)}^2}.3^x$

C. $f\text{'}\left(x\right)=\frac{2}{{\left(3^x+1\right)}^2}.3^x.\ln 3$

D. $f\text{'}\left(x\right)=-\frac{2}{{\left(3^x+1\right)}^2}.3^x.\ln 3$