Question

Tìm A biết:

A=1/1x2+1/2x3+1/3x4+.....+1/18x19+1/19x20

Answer 1

A=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+....+1/19-1/20

A=1-1/20

A=20/20-1/20

A=19/20

Answer 2

19/20 nha ban 

             tich nha

Answer 3

19/20! Nhớ trả lời lại các câu hỏi của mình nhé, buồn quá rồi.

Answer 4

A=1/1x2+1/2x3+1/3x4+.....+1/18x19+1/19x20

A=1-1/20

A=20/20-1/20

A=19/20

Answer 5

A=1/1x2+1/2x3+1/3x4+.....+1/18x19+1/19x20

A=1-1/20

A=20/20-1/20

A=19/20

Answer 6

\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{18.19}+\frac{1}{19.20}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{18}-\frac{1}{19}+\frac{1}{19}-\frac{1}{20}\)

\(=1-\frac{1}{20}\)

\(=\frac{19}{20}\)