D. 8

Đáp án D

Phương pháp:

\(\left( {\frac{1}{{{{\left( {u\left( x \right)} \right)}^n}}}} \right) = \frac{{ - n.\left( {u\left( x \right)} \right)'}}{{{{\left( {u\left( x \right)} \right)}^{n + 1}}}}\)

Cách giải:

\(f\left( x \right) = \frac{1}{{2x - 1}} \Rightarrow f'\left( x \right) = \frac{{ - 2}}{{{{\left( {2x - 1} \right)}^2}}} \Rightarrow f''\left( x \right) = \frac{8}{{{{\left( {2x - 1} \right)}^3}}} \Rightarrow f''\left( 1 \right) = 8\)