Đáp án + Giải thích các bước giải:
Ta có :
`C=\frac{2}{1.4}+\frac{2}{4.7}+\frac{2}{7.10}+...+\frac{2}{46.49}`
`→\frac{3C}{2}=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{46.49}`
`→\frac{3C}{2}=\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{46}-\frac{1}{49}`
`→\frac{3C}{2}=\frac{1}{1}-\frac{1}{49}`
`→\frac{3C}{2}=\frac{48}{49}`
`→3C=\frac{96}{49}`
`→C=\frac{32}{49}`
Vậy `C=\frac{32}{49}`
