Đạo hàm của hàm số f(x)=3^x-1/ 3^x+1

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