=2/6.7+2/7.8+...+2/x(x+1)=2/9
=>1/6-1/7+1/7-1/8+...+1/x-1/x+1=1/9
=>1/6-1/x+1=1/9
=>x=17
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Các câu hỏi tương tự
tính 1/21+1/28+1/36+...+2/x.(x+1) = 2/9
1/21+1/28+1/36+...+2/x(x+1)=2/9
1/21 + 1/28 +1/36 +... + 2/x(x+1) = 2/9
1/21+1/28+1/36+...+2/x(x+1)=2/9
Tìm x: 1/21+1/28+1/36+...+2/x.(x+1)=2/9
b. 1/21+1/28+1/36+...+2/x.(x+1)=2/9
b. 1/21+1/28+1/36+...+2/x.(x+1)=2/9
1/21 + 1/28 + 1/36 +...+ 2/x(x+1) = 2/9
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tìm x
1/21+1/28+1/36+...+2/x(x+1)=2/9