1. Tính
K = \(\frac{1}{7}\)+\(\frac{1}{91}\)+\(\frac{1}{247}\)+\(\frac{1}{475}\)+\(\frac{1}{755}\)+\(\frac{1}{1147}\)
2. Chứng minh rằng
\(\frac{1}{4}\)+\(\frac{1}{16}\)+\(\frac{1}{36}\)+\(\frac{1}{64}\)+\(\frac{1}{100}\)+\(\frac{1}{144}\)+\(\frac{1}{196}\)<\(\frac{1}{2}\)