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Có:
- 2003A=20032004+2003/20032004+1 = 20032004+1+2002/20032004+1= 1+ 2002/20032004+1
- 2003A= 20032003+2003/20032003+1 .........= 1 + 2002/20032003+1
- Vì 1+ 2002/20032004+1<1+ 20022003+1nên 2003A<2003B
- Nên A<B
- !!!!!!!!!!!
\(B=4+3^2+3^3+...+3^{2004}\)
\(\Rightarrow B=1+3+3^2+3^3+...+3^{2004}\)
\(\Rightarrow3B=3+3^2+3^3+...+3^{2005}\)
\(\Rightarrow3B-B=3+3^2+3^3+...+3^{2005}-1-3-3^2-...-3^{2004}\)
\(\Rightarrow2B=3^{2005}-1\)
\(\Rightarrow B=\frac{3^{2005}-1}{2}< \frac{3^{2005}}{2}< 3^{2005}=C\)
Vậy B < C
a/
$A-3=\frac{2003}{2004}+\frac{2004}{2005}+\frac{2005}{2003}-3$
$=(1-\frac{1}{2004})+(1-\frac{1}{2005})+(1+\frac{2}{2003})-3$
$=\frac{2}{2003}-\frac{1}{2004}-\frac{1}{2005}$
$=(\frac{1}{2003}-\frac{1}{2004})+(\frac{1}{2003}-\frac{1}{2005})$
$>0+0=0$
$\Rightarrow A>3$
b/
$B=\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+....+\frac{1}{2015^2}$
$< \frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2014.2015}$
$=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2014}-\frac{1}{2015}$
$=1-\frac{1}{2015}<1$
\(2^{2004}=2^{2001}.2^3=2^{2001}.8\)
\(3^{2003}=3^{2001}.3^2=3^{2001}.9\)
\(2^{2001}.8>3^{2001}.9\)
\(=>2^{2004}<3^{2003}\)
nho li-ke nha