Question

1/1x2+1/2x3+1/3x4+...+1/9x10

Answer 1

Ta đặt biểu thức là:

A = 1/1 x 2 + 1/2 x 3 + 1/3 x 4 + .... + 1/9 x 10

A = 1 - 1/2 + 1/2 - 1/3 +1/3 - 1/4 + ... + 1/9 - 1/10

A = 1 - 1/10

A = 9/10

Answer 2

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{9}-\frac{1}{10}\)

\(=1-\frac{1}{10}\)

\(=\frac{9}{10}\)

Answer 3

 = 1/1 x 2 + 1/2 x 3 + 1/3 x 4 + .... + 1/9 x 10

 = 1 - 1/2 + 1/2 - 1/3 +1/3 - 1/4 + ... + 1/9 - 1/10

 = 1 - 1/10

 = 9/10

Answer 4

1/1x2 + 1/2x3 + 1/3x4 +...+ 1/9x10

Đặt A = 1/1x2 + 1/2x3 + 1/3x4 + ... + 1/9x10

A = 1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/9 - 1/10

A = 1/1 - 1/10

A = 9/10 

Vậy A = 9/10

Answer 5

\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{9.10}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)

\(=1-\frac{1}{10}\)

\(=\frac{9}{10}\)