10000 câu trắc nghiệm tổng hợp môn Toán 2025 mới nhất (có đáp án) - Phần 1

Tìm x

3/726

Tìm x, biết:

\[\left( {\frac{1}{2} + \frac{1}{3} + \frac{1}{4} + ... + \frac{1}{{2014}}} \right) \cdot x = \frac{{2013}}{1} + \frac{{2012}}{2} + \frac{{2011}}{3} + ... + \frac{2}{{2012}} + \frac{1}{{2013}}\].

0/3000 ký tự
Giải thích

Ta có:

\[\frac{{2013}}{1} + \frac{{2012}}{2} + \frac{{2011}}{3} + ... + \frac{2}{{2012}} + \frac{1}{{2013}}\]

\[ = \left( {1 + \frac{{2012}}{2}} \right) + \left( {1 + \frac{{2011}}{3}} \right) + ... + \left( {1 + \frac{2}{{2012}}} \right) + \left( {1 + \frac{1}{{2013}}} \right) + 1\]

\[ = \frac{{2014}}{2} + \frac{{2014}}{3} + ... + \frac{{2014}}{{2012}} + \frac{{2014}}{{2013}} + \frac{{2014}}{{2014}}\]

\[ = 2014 \cdot \left( {\frac{1}{2} + \frac{1}{3} + ... + \frac{1}{{2012}} + \frac{1}{{2013}} + \frac{1}{{2014}}} \right)\]

Nên từ đề bài, ta có:

\[\left( {\frac{1}{2} + \frac{1}{3} + ... + \frac{1}{{2012}} + \frac{1}{{2013}} + \frac{1}{{2014}}} \right) \cdot x = 2014 \cdot \left( {\frac{1}{2} + \frac{1}{3} + ... + \frac{1}{{2012}} + \frac{1}{{2013}} + \frac{1}{{2014}}} \right)\]

Suy ra x = 2014.