1) =1/2 x 2/3 x 3/4 x 4/5 x .... x 2002/2003 x 2003/2004

=1/2004

2) 1/2 x X-3/4=5/6

1/2 x X =3/4+5/6

1/2 x X =19/12

X=19/6

\(\left(1-\frac{1}{2}\right).\left(1-\frac{1}{3}\right).\left(1-\frac{1}{4}\right)...\left(1-\frac{1}{2003}\right).\left(1-\frac{1}{2004}\right)\)

\(=\frac{1}{2}.\frac{2}{3}.\frac{3}{4}...\frac{2002}{2003}.\frac{2003}{2004}\)

\(=\frac{1.2.3...2002.2003}{2.3.4...2003.2004}=\frac{1}{2004}\)

\(\frac{1}{2}.x-\frac{3}{4}=\frac{5}{6}\)

\(\frac{1}{2}.x=\frac{5}{6}+\frac{3}{4}\)

\(\frac{1}{2}.x=\frac{10}{12}+\frac{9}{12}=\frac{19}{12}\)

\(x=\frac{19}{12}:\frac{1}{2}\)

\(x=\frac{19}{12}.2=\frac{19}{6}\)

(1-1/2) x (1-1/3) x (1-1/4) x...x (1-1/2004)

=1/2 x 2/3 x 3/4 x ... x 2002/2003 x 2003/2004 = 1/2004

1/2 x X -3/4 = 5/6

=> 1/2 x X = 5/6 +3/4 = 19/12

=> x= 19/12 : 1/2

=> x=19/6

a) \(\frac{x-1}{2015}+\frac{x-2}{2014}=\frac{x-3}{2013}+\frac{x-4}{2012}\)

\(\Rightarrow\left(\frac{x-1}{2015}-1\right)+\left(\frac{x-2}{2014}-1\right)=\left(\frac{x-3}{2013}-1\right)+\left(\frac{x-4}{2012}-1\right)\)

\(\Rightarrow\frac{x-2016}{2015}+\frac{x-2016}{2014}=\frac{x-2016}{2013}+\frac{x-2016}{2012}\)

\(\Rightarrow\frac{x-2016}{2015}+\frac{x-2016}{2014}-\frac{x-2016}{2013}-\frac{x-2016}{2012}=0\)

\(\Rightarrow\left(x-2016\right).\left(\frac{1}{2015}+\frac{1}{2014}-\frac{1}{2013}-\frac{1}{2012}\right)=0\)

Vì \(\frac{1}{2015}+\frac{1}{2014}-\frac{1}{2013}-\frac{1}{2012}\ne0\Rightarrow x-2016=0\)

\(\Rightarrow x=2016\)

b) \(\frac{x-1}{2004}+\frac{x-2}{2003}-\frac{x-3}{2002}=\frac{x-4}{2001}\)

\(\Rightarrow\frac{x-1}{2004}+\frac{x-2}{2003}-\frac{x-3}{2002}-\frac{x-4}{2001}=0\)

\(\Rightarrow\left(\frac{x-1}{2004}-1\right)+\left(\frac{x-2}{2003}-1\right)-\left(\frac{x-3}{2002}-1\right)-\left(\frac{x-4}{2001}-1\right)=0\)

\(\Rightarrow\frac{x-2005}{2004}+\frac{x-2005}{2003}-\frac{x-2005}{2002}-\frac{x-2005}{2001}=0\)

\(\Rightarrow\left(x-2005\right)\left(\frac{1}{2004}+\frac{1}{2003}-\frac{1}{2002}-\frac{1}{2001}\right)=0\)

vì \(\frac{1}{2004}+\frac{1}{2003}-\frac{1}{2002}-\frac{1}{2001}\ne0\Rightarrow x-2005=0\)

\(\Rightarrow x=2005\)

c) \(|5x-3|\ge7\)

\(\Rightarrow5x-3\ge7\) hoặc - (5x-3) \(\ge7\)

\(\Rightarrow5x-3\ge7\) hoặc \(-5x+3\ge7\)

\(\Rightarrow5x\ge10\) hoặc \(-5x\ge4\)

\(\Rightarrow x\ge2\) hoặc \(x\le\frac{4}{-5}\)

k nhé!!! Kp luôn nha!

Giúp mình nhanh nha! Mình sẽ thick người đó

\(\text{Ta có:}2;6;10;...;8010\text{ đều chia 4 dư 2}\)

\(\Rightarrow X\equiv2^2+3^2+4^2+....+2004^2\left(mod\text{ }10\right)\)

\(\text{ mà:}1^2+2^2+3^2+....+2004^2=\frac{2004.2005.4009}{6}=333.2005.4009\)

\(\Rightarrow X\equiv333.2005.4009-1\left(\text{mod 10}\right)\equiv3.5.9-1\equiv4\left(\text{mod 10}\right)\)

Vậy X có chữ số tận cùng là 4

\(1+\frac{1}{2}+\frac{1}{3}+....+\frac{1}{2^{10}-1}\)

\(< 1+\frac{1}{2}+\frac{1}{2}+\left(\frac{1}{2^2}+\frac{1}{2^2}+\frac{1}{2^2}+\frac{1}{2^2}\right)+..........\left(\frac{1}{2^9}+\frac{1}{2^9}+....+\frac{1}{2^9}\left(\text{512 số hạng }\frac{1}{2^9}\right)\right)\)

\(=1+1+1+1+1+1+1+1+1+1\)

\(=10\left(\text{điều phải chứng minh}\right)\)

\(\text{bài 2 câu b tương tự câu a}\)

câu 2 mình chưa hiểu lắm bạn có thể giải thích cho mình được không ạ? Mình cảm ơn ạ ^^

x+4/2001+x+3/2002=-x+2/2003+x+1/2004

x=...

\(\frac{x+4}{2001}+\frac{x+3}{2002}=\frac{x+2}{2003}+\frac{x+1}{2004}\)

\(\Leftrightarrow\left(\frac{x+4}{2001}+1\right)+\left(\frac{x+3}{2002}+1\right)=\left(\frac{x+2}{2003}+1\right)+\left(\frac{x+1}{2004}+1\right)\)

\(\Leftrightarrow\frac{x+2005}{2001}+\frac{x+2005}{2002}=\frac{x+2005}{2003}+\frac{x+2005}{2004}\)

\(\Leftrightarrow\frac{x+2005}{2001}+\frac{x+2005}{2002}-\frac{x+2005}{2003}-\frac{x+2005}{2004}=0\)

\(\Leftrightarrow\left(x+2005\right).\left(\frac{1}{2001}+\frac{1}{2002}+\frac{1}{2003}+\frac{1}{2004}\right)=0\)

Vì  \(\left(\frac{1}{2001}+\frac{1}{2002}+\frac{1}{2003}+\frac{1}{2004}\right)\ne0\)

\(\Rightarrow x+2004=0\)

\(\Rightarrow x=0-2004=-2004\)

\(\left(x-\frac{1}{2004}\right)+\left(x-\frac{2}{2003}\right)-\left(x-\frac{3}{2002}\right)=x-\frac{4}{2001}\)

\(x-\frac{1}{2004}+x-\frac{2}{2003}-x+\frac{3}{2002}-x=-\frac{4}{2001}\)

\(x+x-x-x-\frac{1}{2004}-\frac{2}{2003}+\frac{3}{2002}=-\frac{4}{2001}\)

\(0x-\frac{1}{2004}-\frac{2}{2003}+\frac{3}{2002}=-\frac{4}{2001}\)

\(\Rightarrow\) Vô lý

Vậy \(x\in\phi\)

đúng ko zay

ko hieu de x-1 hay la xhi x-

\(\frac{x-1}{2004}+\frac{x-2}{2003}=\frac{x-3}{2002}+\frac{x-4}{2001}\)

\(\Rightarrow\frac{x-1}{2004}-1+\frac{x-2}{2003}-1=\frac{x-3}{2002}-1+\frac{x-4}{2001}-1\)

\(\Rightarrow\frac{x-2005}{2004}+\frac{x-2005}{2003}=\frac{x-2005}{2002}+\frac{x-2005}{2001}\)

\(\Rightarrow\frac{x-2005}{2001}+\frac{x-2005}{2002}-\frac{x-2005}{2003}-\frac{x-2005}{2004}=0\)

\(\Rightarrow\left(x-2005\right).\left(\frac{1}{2001}+\frac{1}{2002}-\frac{1}{2003}-\frac{1}{2004}\right)=0\)

Vì \(\frac{1}{2001}>\frac{1}{2003};\frac{1}{2002}>\frac{1}{2004}\)

\(\Rightarrow\frac{1}{2001}+\frac{1}{2002}-\frac{1}{2003}-\frac{1}{2004}\ne0\)

\(\Rightarrow x-2005=0\)

\(\Rightarrow x=2005\)

x+2005=0