Question

1. Tính các tổng sau 

      A=1/4*5+1/5*6+1/6*7+...+1/99*100

      B=3/5*7+3/7*9+...+3/51*53

 

 

Answer 1

A=1/4*5+1/5*6+1/6*7+...+1/99*100

\(A=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{99}-\frac{1}{100}\)

\(=\frac{1}{4}-\frac{1}{100}\)

\(=\frac{6}{25}\)

Answer 2

A = 1/4 - 1/5 + 1/5 - 1/6 + ..... + 1/99 - 1/100

   = 1/4 - 1/100

    = 6/25

B  xem lại đề phép cuối