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\(S=\frac{1}{2^2}-\frac{1}{2^4}+\frac{1}{2^6}-....+\frac{1}{2^{4n-2}}-\frac{1}{2^{4n}}+...+\frac{1}{2^{2002}}-\frac{1}{2^{2004}}\)
\(<\frac{1}{2^4}-\frac{1}{2^4}+\frac{1}{2^8}-\frac{1}{2^8}+...+\frac{1}{2^{4n}}-\frac{1}{2^{4n}}+...+\frac{1}{2^{2004}}-\frac{1}{2^{2004}}\)=0+0+0+...+0+....+0=0 <0,2
Vậy S<0,2
Ta có :
Tử số = \(\frac{2006}{2}+...+\frac{2006}{2007}\)
= 2006.(\(\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2007}\))
MS= \(\frac{2006}{1}+\frac{2005}{2}+...+\frac{1}{2006}\)
= 2006+\(\frac{2007-2}{2}+\frac{2007-3}{3}+...+\frac{2007-2006}{2006}\)
=200+.(\(\frac{2007}{2}+\frac{2007}{3}+...+\frac{2007}{2006}\)) - ( 1+1+1+...+1 )(2006c/s1)
= 2006 . (\(\frac{2007}{2}+...+\frac{2007}{2006}\))-2006
=\(\frac{2007}{2}+...+\frac{2007}{2006}\)
=2007.(\(\frac{1}{2}+...+\frac{1}{2006}\))
Khi đó :
C= .... bạn tự đáp số
và cuối cùng C = \(\frac{2006}{2007}\)
A=\(\frac{\frac{3}{7}-\frac{3}{17}+\frac{3}{37}}{\frac{5}{7}-\frac{5}{17}+\frac{5}{37}}+\frac{\frac{1}{2}-\frac{1}{3}+\frac{1}{4}-\frac{1}{5}}{\frac{7}{5}-\frac{7}{4}+\frac{7}{3}-\frac{7}{2}}\)
\(=\frac{3\left(\frac{1}{7}-\frac{1}{17}+\frac{1}{37}\right)}{5\left(\frac{1}{7}-\frac{1}{17}+\frac{1}{37}\right)}+\frac{\frac{1}{2}-\frac{1}{3}+\frac{1}{4}-\frac{1}{5}}{-7\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{4}-\frac{1}{5}\right)}\)
\(=\frac{3}{5}+\frac{1}{-7}=\frac{3}{5}-\frac{1}{7}\)
\(=\frac{21}{35}-\frac{5}{35}=\frac{16}{35}\)
Ta có, với \(n\) nguyên dương: \(1+2+...+n=\frac{n\left(n+1\right)}{2}\)
Suy ra, \(1-\frac{1}{1+2+...+n}=1-\frac{2}{n\left(n+1\right)}=\frac{\left(n-1\right)\left(n+2\right)}{n\left(n+1\right)}\)
Khi đó:
\(1-\frac{1}{1+2}=\frac{1.4}{2.3}\)
\(1-\frac{1}{1+2+3}=\frac{2.5}{3.4}\)
....
\(1-\frac{1}{1+2+...+2013}=\frac{2012.2015}{2013.2014}\)
\(1-\frac{1}{1+2+...+2014}=\frac{2013.2016}{2014.2015}\)
Suy ra, \(P=\frac{\left(1.2.....2013\right).\left(4.5.....2016\right)}{2.\left(3.4.....2014\right)^2.2015}=\frac{2016}{3.2014}=\frac{336}{1007}\)
B=3/2 xin loi nha
vì cách trình bày trên này khó quá, đọc chắc bạn ko hiểu đâu
\(\frac{24\cdot47-23}{24+47\cdot23}.\frac{3+\frac{3}{7}-\frac{3}{11}+\frac{3}{1001}-\frac{3}{13}}{\frac{9}{1001}-\frac{9}{13}+\frac{9}{7}-\frac{9}{11}+9}\)
\(=\frac{24\cdot\left(24+23\right)-23}{24+\left(24+23\right)\cdot23}\cdot\frac{3\left(1+\frac{1}{7}-\frac{1}{11}+\frac{1}{1001}-\frac{1}{13}\right)}{9\left(\frac{1}{1001}-\frac{1}{13}+\frac{1}{7}-\frac{1}{11}+1\right)}\)
\(=\frac{24^2+24\cdot23-23}{24+24\cdot23+23^2}\cdot\frac{3}{9}\) \(=\frac{24^2+23\cdot\left(24-1\right)}{\left(23+1\right)\cdot24\cdot23^2}\cdot\frac{1}{3}=1\cdot\frac{1}{3}=\frac{1}{3}\)
đặt \(A=\frac{2004}{1}+\frac{2003}{2}+\frac{2002}{3}+...+\frac{1}{2004}\)
\(A=\left(\frac{2003}{2}+1\right)+\left(\frac{2002}{3}+1\right)+..+\left(\frac{1}{2004}+1\right)+\frac{2005}{2005}\)
\(A=\frac{2005}{2}+\frac{2005}{3}+..+\frac{2005}{2004}+\frac{2005}{2005}\)
\(A=2005.\left(\frac{1}{2}+\frac{1}{3}+..+\frac{1}{2004}+\frac{1}{2005}\right)\)
\(P=\frac{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+..+\frac{1}{2005}}{A}=\frac{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+..+\frac{1}{2005}}{2005.\left(\frac{1}{2}+\frac{1}{3}+..+\frac{1}{2005}\right)}=\frac{1}{2005}\)
vậy P=1/2005
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