Question

Tính A biết A=1/2+1/6+1/12+...+1/6480

giup minh nhanh len nhe minh dang can

 

Answer 1

\(A=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{6480}\)

\(=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{80.81}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{80}-\frac{1}{81}=1-\frac{1}{81}=\frac{80}{81}\)

Answer 2

\(A=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{6480}\)

\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{80.81}\)

\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{80}-\frac{1}{81}\)

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

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

Cái này là toán lớp 6 nha bn

Ủng hộ mk nha ^_-

Answer 3

A=\(\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}+...+\frac{1}{80x81}\)

A=\(1-\frac{1}{81}=\frac{80}{81}\)

Answer 4

Ta có:

\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{80.81}\)

\(A=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{80}-\frac{1}{81}\)

\(A=1-\frac{1}{81}=\frac{80}{81}\)

Answer 5

\(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{80\cdot81}\)

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

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

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