1. Chứng minh rằng : A=\(\frac{1}{9}\)+\(\frac{1}{16}\)+\(\frac{1}{25}\)+.......+\(\frac{1}{2500}\)+\(\frac{1}{4}\)
2.Rút gọn các phân số sau:
A=\(\frac{10\cdot11+50\cdot55+70\cdot77}{11\cdot12+55\cdot60+77\cdot84}\)
B=\(\frac{32768\cdot125\cdot64\cdot81}{8\cdot262144\cdot81\cdot5}\)
Bài 2:
a: \(A=\dfrac{11\cdot10\left(1+5\cdot5+7\cdot7\right)}{11\cdot12\left(1+5\cdot5+7\cdot7\right)}=\dfrac{10}{12}=\dfrac{5}{6}\)
\(B=\dfrac{1}{8}\cdot\dfrac{125}{5}\cdot\dfrac{81}{81}\cdot\dfrac{64}{8}=25\)