1+1/3+1/6+1/10+......+2/x×(x+1)=4032/2017
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Xét đa thức
\(P\left(x\right)=\left(1-x+x^2-x^3+...-x^{2015}+x^{2016}\right)\left(1+x+x^2+x^3+...+x^{2015}+x^{2016}\right)\)
Khai triển và ước lượng các hạng tử đồng dạng có thể viết
\(P\left(x\right)=a_0+a_1x+a_2x^2+...+a_{4032}x^{4032}\)Tính \(a_{2017}\)
Tìm x biết :1/3+1/6+1/10+...+2/x(x+1) =2015/2017
1/3+1/6+1/10+...+2/x(x+1)=2015/2017. tìm stn x
Tim x:
1/3+1/6+1/10+...+2/x(x+1)=2015/2017
\(\frac{2}{6}+\frac{2}{12}+...+\frac{2}{x\left(x+1\right)}=\frac{2015}{2017}\)
\(2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{x}-\frac{1}{x+1}\right)=\frac{2015}{2017}\)
\(2\left(\frac{1}{2}-\frac{1}{x+1}\right)=\frac{2015}{2017}\)
\(\frac{1}{2}-\frac{1}{x+1}=\frac{2015}{2017}:2\)
\(\frac{1}{x+1}=\frac{1}{2}-\frac{2015}{4034}\)
\(\frac{1}{x+1}=\frac{1}{2017}\)
=>x+1=2017
=>x=2016
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\(\frac{2}{6}+\frac{2}{12}+...+\frac{2}{x\left(x+1\right)}=\frac{2015}{2016}\)
\(2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{x}-\frac{1}{x+1}\right)=\frac{2015}{2016}\)
\(2\left(\frac{1}{2}-\frac{1}{x+1}\right)=\frac{2015}{2016}\)
\(\frac{1}{2}-\frac{1}{x+1}=\frac{2015}{2016}:2\)
\(\frac{1}{x+1}=\frac{1}{2}-\frac{2015}{4032}\)
\(\frac{1}{x+1}=\frac{1}{4032}\)
=>x+1=4032
=>x=4031
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tìm x
1/3 + 1//6 + 1/10 + . . . . +1/x^2/2=2017/2016
tìm số tự nhiên x biêt rằng:1/3+1/6+1/10+.......+2/x(x+1)=2015/2017
Tìm số tự nhiên x biết rằng: 1/3+1/6+1/10+...+2/x(x+1)=2015/2017
= 2/(2.3) + 2/3.4 + 2/4.5 +...+ 2/x(x+1)
= 2 [1/2-1/3+1/3-1/4+...+1/x-1/(x+1)]
=2[1/2-1/(x+1)]= (x-1)/(x+1)
= 2001/2003
==> x=2002
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1+1/3+1/6+1/10+...+2/x.(x+1)=1/2015/2017 (hỗn số)
\(1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{2}{x.\left(x+1\right)}=1\frac{2015}{2017}\)
\(\frac{2}{2}+\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+...+\frac{2}{x.\left(x+1\right)}=\frac{4032}{2017}\)
\(2.\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{x.\left(x+1\right)}\right)=\frac{4032}{2017}\)
\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{x.\left(x+1\right)}=\frac{4032}{2017}:2\)
\(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{x}-\frac{1}{x+1}=\frac{4032}{2017}.\frac{1}{2}\)
\(1-\frac{1}{x+1}=\frac{2016}{2017}\)
\(\frac{x}{x+1}=\frac{2016}{2017}\)
=> \(x=2016\)
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Tim so tu nhienx,biet rang:1/3+1/6+1/10+...+2/x•(x+1)=2015/2017
Theo đầu bài ta có:
\(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{2}{x\left(x+1\right)}=\frac{2015}{2017}\)
\(\Rightarrow\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+...+\frac{2}{x\left(x+1\right)}=\frac{2015}{2017}\)
\(\Rightarrow2\cdot\left(\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+...+\frac{1}{x\left(x+1\right)}\right)=\frac{2015}{2017}\)
\(\Rightarrow\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{x}-\frac{1}{x+1}=\frac{2015}{4034}\)
\(\Rightarrow\frac{1}{2}-\frac{1}{x+1}=\frac{2015}{4034}\)
\(\Rightarrow\frac{1}{x+1}=\frac{1}{2017}\)
\(\Rightarrow x+1=2017\)
\(\Rightarrow x=2016\)
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\(\frac{2}{6}\)\(+\frac{2}{12}\)\(+...+\frac{2}{x\left(x+1\right)}=\frac{2015}{2017}\)
\(2\left(\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{x}-\frac{1}{x+1}\right)=\frac{2015}{2017}\)
\(2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{x}-\frac{1}{x+1}\right)=\frac{2015}{2017}\)
\(\frac{1}{2}-\frac{1}{x+1}=\frac{2015}{2017}\div2\)
\(\frac{1}{x+1}=\frac{1}{2}-\frac{2015}{4034}\)
\(\frac{1}{x+1}=\frac{1}{2017}\)
\(=>x+1=2017\)
\(=>x=2016\)
Chúc bạn học tốt Vu_anh_tuan !
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