Question

tính tổng : 

A=1/1.2+1/2.3+...+1/49.50

Answer 1

A = 1 - 1/2 + 1/2 - 1/3 + ............. + 1/49 - 1/50

A = 1 - 1/50

A = 49/50

Chúc bạn học giỏi

Answer 2

Ta có: A = 1/1.2 + 1/2.3 +... + 1/49.50

A = 1 -1/2 +1/2 -1/3 +... + 1/49 -1/50

A = 1 - 1/50

A = 49/50

Answer 3

\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+.....+\frac{1}{49}-\frac{1}{50}=\frac{49}{50}..\)

Answer 4

\(A=\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{49.50}\)

\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{49}-\frac{1}{50}\)

\(A=1-\frac{1}{50}\)

\(A=\frac{49}{50}\)

Answer 5

Đặt \(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{49.50}\)
\(=2-\frac{1}{1.2}+3-\frac{2}{2.3}+4-\frac{3}{3.4}+...+50-\frac{49}{49}\)
\(=\frac{2}{1.2}-\frac{1}{1.2}+\frac{3}{2.3}-\frac{2}{2.3}+\frac{4}{3.4}+...+\frac{51}{49.50}-\frac{49}{49.50}\) 
\(=1-\frac{1}{50}\)
\(=\frac{49}{50}\)
Vậy giá trị của biểu thức \(A\) là \(\frac{49}{50}\)