Gọi tổng trên là A
1/2A= 2/1.3+1/3.5+...+1/x.(x+2)
1/2A= 1-1/x.(x+2)
A=\(\frac{1-\frac{1}{x.\left(x+2\right)}}{2}\)
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Các câu hỏi tương tự
1/1.3 + 1/3.5 + 1/5.7 +...+ 1/x.(x+2) = 20/41
a,1/1.3+1/3.5+1/5.7+......+1/x+(x+2)=20/41
b,1/3+1/6+1/10+....+1/x.(x+1:2)=2009/2011
c,1/21+1/28+1/36+...+2/x.x+1=2/9
Tìm x biết : 1/1.3+ 1/3.5+ 1/5.7+...+ 1/x.(x+2)=50/101.
a) 1/1.3+1/3.5+1/5.7
b) 1/1.3+1/3.5+1/5.7+...+1/2007.2009+1/2009.2011
Tìm y : ( 1/1.3 + 1/3.5 + 1/5.7 + 1/7.9 + 1/9.11 ) .y = 2/3.
1/1.3+1/3.5+1/5.7+...+1/99.101
S=1/1.3+1/3.5+1/5.7+...+1/99.100
A=1/1.3+1/3.5+1/5.7+....+1/99.101
1/1.3+1/3.5+1/5.7+...+1/2007.2009+1/2009.2010