Question

Cho S = 1/1.3 + 1/3.5 +1/5.7 + ......+ 1/99.101. Khi đó  2S + 1/101 = ?

Answer 1

2S=2/1.3+2/3.5+....+2/99.101

2S=1-1/3+1/3-1/5+....+1/99-1/101

2S=1-1/101

2S+1/101=1-1/101+1/101=1

Nho tick nha

Answer 2

\(S=\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{99.101}\)

\(S=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{99}-\frac{1}{101}\)

\(S=1-\frac{1}{101}=\frac{100}{101}\)

\(2S+\frac{1}{101}=\frac{100}{101}\)

\(S=2.\frac{100}{101}+\frac{1}{101}\)

\(\Rightarrow S=\frac{201}{101}\)

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Answer 3

2S + \(\frac{1}{101}\)=\(\frac{201}{101}\)

Answer 4

2S + \(\frac{1}{101}\)= \(\frac{201}{101}\)

Answer 5

Lê Phương Thảo sai rồi bạn

Phải thế này:

  S = 1/1.3 + 1/3.5 + 1/5.7 +....+ 1/99.101

2S = 2/1.3 + 2/3.5 + 2/5.7 +....+ 2/99.101

2S = 1 - 1/3 + 1/3 - 1/5 +1/5 - 1/7 +....+ 1/99 - 1/101

2S = 1 - 1/101 = 100/101 

  S = 100/101 : 2 = 100/101 . 1/2 = 50/101

 Cô giáo mình dạy thế nhé !