Question

tinh hop ly a=1/1*2+1/2*3+...+1/9*10

Answer 1

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

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

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

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

Answer 2

A = 1/1.2 + 1/2.3 + 1/3.4 + .. + 1/9.10

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

A = 1 - 1/10

A = 9/10

Answer 3

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

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

   \(=1-\frac{1}{10}\)

   \(=\frac{9}{10}\)