Question

[Yumy Kang]

Tìm số tự nhiên x, thỏa mãn:

a) \(\frac{x}{2008}\)- \(\frac{1}{10}\)- \(\frac{1}{15}\)- \(\frac{1}{21}\)- ... - \(\frac{1}{120}\)=\(\frac{5}{8}\)

b) \(\frac{7}{x}\)+\(\frac{4}{5.9}\)+\(\frac{4}{9.13}\)+\(\frac{4}{13.17}\)+...+\(\frac{4}{41.45}\)=\(\frac{29}{45}\)

c) \(\frac{1}{3.5}\)+\(\frac{1}{5.7}\)+\(\frac{1}{7.9}\)+...+\(\frac{1}{\left(2x+1\right)\left(2x+3\right)}\)=\(\frac{15}{93}\)

Answer 1

[chu Dinh Tuyen]

bai kho hieu the

Answer 2

[Pham Hong Quan]

mình trả lời cho câu c nhé

c,\(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2x+1}-\frac{1}{2x+3}=\frac{15}{93}\)

\(\Rightarrow\)\(\frac{1}{3}-\frac{1}{2x+3}=\frac{15}{93}\)

\(\Rightarrow\)\(\frac{1}{2x+3}=\frac{31}{93}-\frac{15}{93}=\frac{16}{93}\)

\(\Rightarrow\frac{16}{32x+48}=\frac{16}{93}\)

\(\Rightarrow32x=45\)

\(\Rightarrow x=\frac{45}{32}\)