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