A = \(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...........+\frac{1}{49.50}+\frac{1}{50.51}\)

   = \(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-........+\frac{1}{49}-\frac{1}{50}+\frac{1}{50}-\frac{1}{51}\)

   = \(1-\frac{1}{51}=\frac{50}{51}\)

tách mẫu ra thì nó sẽ là tích hai số tự nhiên liên tiếp liền nhau. 

49/303

50/51

\(A=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{2450}+\frac{1}{2550}\)

\(A=\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}+\frac{1}{4x5}+...+\frac{1}{49x50}+\frac{1}{50x51}\)

\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{49}-\frac{1}{50}+\frac{1}{50}-\frac{1}{51}\)

\(A=1-\frac{1}{51}=\frac{50}{51}\)

50/51

50/51

dap an da dung roi

A=1/1x2+1/2x3+1/3x4+1/4x5+...+1/49x50+1/50x51

A=2-1/1x2+3-2/2x3+4-3/3x4+...+50-49/49x50+51-50/50x51

A=1-1/2+1/2-1/3+1/3+1/4+...-1/49+1/49-1/50+1/50-1/51

A=1-1/51

A=51/51-1/51

A=50/51

tick nha

cách giải thế nào rồi mình an tick cho

A=\(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+...+\frac{1}{50\cdot51}\)

A=\(\left(\frac{1}{1}-\frac{1}{2}\right)+\left(\frac{1}{2}-\frac{1}{3}\right)+...+\left(\frac{1}{50}-\frac{1}{51}\right)\)

A=\(1-\frac{1}{51}\)

A=\(\frac{50}{51}\)

50/51

50/51