(2/11*13+2/13*15+2/15*17+2/17*19+2/19*21)*462-x=19 tìm x

Đáp án:

 \(x=1\)

Giải thích các bước giải:

\[\begin{array}{l}
\left( {\frac{2}{{11 \times 13}} + \frac{2}{{13 \times 15}} + \frac{2}{{15 \times 17}} + \frac{2}{{17 \times 19}} + \frac{2}{{19 \times 21}}} \right) \times 462 - x = 19\\
\left( {\frac{1}{{11}} - \frac{1}{{13}} + \frac{1}{{13}} - \frac{1}{{15}} + \frac{1}{{15}} - \frac{1}{{17}} + \frac{1}{{17}} - \frac{1}{{19}} + \frac{1}{{19}} - \frac{1}{{21}}} \right) \times 462 - x = 19\\
\left( {\frac{1}{{11}} - \frac{1}{{21}}} \right) \times 462 - x = 19\\
\frac{{10}}{{231}} \times 462 - x = 19\\
20 - x = 19\\
x = 20 - 19\\
x = 1
\end{array}\]