Question

1/1+3   +   1/1+3+5     +          …….      +       1/1+3+5+…+19+21

Answer 1

ko biết

 

Answer 2

là sao bn nhỉ?

Answer 3

\(\dfrac{1}{1+3}+\dfrac{1}{1+3+5}+...+\dfrac{1}{1+3+5+...+19+21}\)

\(=\dfrac{1}{2^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+\dfrac{1}{5^2}+\dfrac{1}{6^2}+\dfrac{1}{7^2}+\dfrac{1}{8^2}+\dfrac{1}{9^2}+\dfrac{1}{10^2}+\dfrac{1}{11^2}\)

\(=\dfrac{1}{4}+\dfrac{1}{9}+\dfrac{1}{16}+\dfrac{1}{25}+\dfrac{1}{36}+\dfrac{1}{49}+\dfrac{1}{64}+\dfrac{1}{81}+\dfrac{1}{100}+\dfrac{1}{121}\)

\(=0,828\)