Question

Tính nhanh

A=\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+....+\frac{1}{132}=?\)

 

Answer 1

A=1/2+1/6+1/12+...+1/132

   =1/1.2+1/2.3+1/3.4+...+1/11.12

   =1/1-1/2+1/2-1/3+1/3-1/4+...+1/11-1/12

   =1-1/12

=11/12

Answer 2

A=1/2+1/6+1/12+...+1/132

   =1/1.2+1/2.3+1/3.4+...+1/11.12

   =1/1-1/2+1/2-1/3+1/3-1/4+...+1/11-1/12

   =1-1/12

   =11/12

Vậy A=11/12