Đáp án và lời giải
Đáp án:A
Lời giải:Ta có: $\begin{gathered} 4000 \times 2002 + 4006 = 4000 \times 2002 + 4004 + 2 \ \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 4000 \times 2002 + 2 \times 2002 + 2 \ \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 2002 \times \left( {4000 + 2} \right) + 2 \ \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 2002 \times 4002 + 2 \ \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 2 \times \left( {2002 \times 2001 + 1} \right) \ \\ \end{gathered} $ Suy ra: $\begin{gathered} A = \frac{{2001 \times 2002 + 1}}{{4000 \times 2002 + 4006}} \ \\ \,\,\,\, = \frac{{2001 \times 2002 + 1}}{{2 \times \left( {2001 \times 2002 + 1} \right)}} \ \\ \,\,\,\, = \frac{1}{2} \ \\ \end{gathered} $ Vậy $A = \frac{1}{2}$.
