Question

tim A biet:

A= 1/2+1/6+1/12+...+1/6480

Answer 1

A=\(\frac{1}{1.2}+\frac{1}{2.3}+.............+\frac{1}{80.81}\)

\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+.........+\frac{1}{80}-\frac{1}{81}\)

\(=1-\frac{1}{81}\)

\(=\frac{80}{81}\)

Answer 2

A = 1/2 + 1/6 + 1/12 + ... + 1/6480

A = 1/1.2 + 1/2.3 + 1/3.4 + ... + 1/80.81 

A = 1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/80 - 1/81

A = 1/1 - 1/81

A = 80/81

Vậy A = 80/81

Answer 3

\(\text{Ta có: }A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+.....+\frac{1}{80.81}\)

\(\Rightarrow A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+......+\frac{1}{80}-\frac{1}{81}\)

\(\Rightarrow A=1-\frac{1}{81}\)

\(\Rightarrow A=\frac{80}{81}\)

Answer 4

=1/1.2+1/2.3+1/3.4+...+1/80.81

=1-1/2+1/2-1/3+...+1/80-1/81

=1-1/81

=80/81

vậy A=80/81

k nha

Answer 5

A=1/1.2+1/2.3+.....+1/80.81

⇒A=1−1/2 +1/2 −1/3 +......+1/80 −1/81 

⇒A=1−1/81 

⇒A=80/81 

Answer 6

A = 1/1.2 + 1/2.3 + 1/3.4 + ... + 1/80.81 

A = 1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/80 - 1/81

A = 1/1 - 1/81

A = 80/81

Vậy A = 80/81