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19 tháng 8 2015

C = 1.2.3.4....2011

D = 1007/2 . 1008/2 . 1009/2.....2012/2

D = (1007.1008.1009.....2012) : (2.2.2.2........2) (có 2012 - 1007 + 1 = 1006 số 2 )

D = (1007.1008.1009....503 .2.2) : 21004

MÀ (4.503.1007.1008.....2011) < (1.2.3.....2011)

Vậy c > D

Ta có: 20082 > 2008-1 = 2007.2009 => 1007/1008<1008/1009

5 tháng 6 2018

Ta có:\(\frac{1007}{1008}=1-\frac{1}{1008}\)

\(\frac{1008}{1009}=1-\frac{1}{1009}\)

mà \(\frac{1}{1008}>\frac{1}{1009}\)

=> \(1-\frac{1}{1008}< 1-\frac{1}{1009}\)

Hay  \(\frac{1007}{1008}< \frac{1008}{1009}\)

Vậy .......

Chúc bạn hk tốt!!! nhớ k cho mình na

4 tháng 4 2015

Ta có:\(1-\frac{1}{2}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2011}-\frac{1}{2012}\)

=\(1+\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{2011}+\frac{1}{2012}-2.\left(\frac{1}{2}+\frac{1}{4}+...+\frac{1}{2012}\right)\)

=\(1+\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2012}-\left(1+\frac{1}{2}+\frac{1}{3}+...+\frac{1}{1006}\right)\)

=\(\frac{1}{1007}+\frac{1}{1008}+...+\frac{1}{2012}\)

=>\(\left(\frac{A}{B}\right)^{2013}\)=(\(\frac{\frac{1}{1007}+\frac{1}{1008}+...+\frac{1}{2012}}{\frac{1}{1007}+\frac{1}{1008}+...+\frac{1}{2012}}^{ }\))2013=12013=1

20 tháng 7 2017

\(\dfrac{x+1}{2014}+\dfrac{x+2}{2013}+.....+\dfrac{x+1007}{1008}=\dfrac{x+1008}{1007}+\dfrac{x+1009}{1006}+........+\dfrac{x+2014}{1}\)\(\Leftrightarrow\left(\dfrac{x+1}{2014}+1\right)+\left(\dfrac{x+2}{2013}+1\right)+...+\left(\dfrac{x+1007}{1008}+1\right)=\left(\dfrac{x+1008}{1007}+1\right)+\left(\dfrac{x+1009}{1006}+1\right)+...+\left(\dfrac{x+2014}{1}+1\right)\)\(\Leftrightarrow\dfrac{x+2015}{2014}+\dfrac{x+2015}{2013}+...+\dfrac{x+1007}{1008}=\dfrac{x+2015}{1007}+\dfrac{x+1009}{1006}+...+\dfrac{x+2014}{1}\)\(\Leftrightarrow\dfrac{x+2015}{2014}+\dfrac{x+2015}{2013}+...+\dfrac{x+2015}{1008}-\dfrac{x+1008}{1007}-\dfrac{x+2015}{1006}-...-\dfrac{x+2015}{1}=0\)\(\Leftrightarrow\left(x+2015\right)\left(\dfrac{1}{2014}+\dfrac{1}{2013}+...+\dfrac{1}{1008}-\dfrac{1}{1007}-\dfrac{1}{1006}-...-1\right)=0\)\(\Leftrightarrow x+2015=0\left(\dfrac{1}{2014}+\dfrac{1}{2013}+...+\dfrac{1}{1008}-\dfrac{1}{1007}-\dfrac{1}{1006}-...-1>0\right)\)\(\Leftrightarrow x=-2015\)

Vậy x=-2015