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22 tháng 8 2017

sai de bai rui 

31 tháng 7 2020

\(\frac{2x-4,36}{0,125}=0,25.42,9-11,7.0,25+0,25.0,8\)

\(\Leftrightarrow\frac{2x-4,36}{0,125}=0,25.\left(42,9-11.7+0,8\right)\)

\(\Leftrightarrow\frac{2x-4,36}{0,125}=0,25.32\)

\(\Leftrightarrow\frac{2x-4,36}{0,125}=8\)

\(\Leftrightarrow2x-4,36=1\)

\(\Leftrightarrow2x=5,36\)

\(\Leftrightarrow x=2,68\)

b) \(N=\frac{1}{1.5}+\frac{1}{5.10}+\frac{1}{10.15}+\frac{1}{15.20}+...+\frac{1}{2005.2010}\)

\(\Leftrightarrow N=\frac{1}{5}\left(1-\frac{1}{5}+\frac{1}{5}-\frac{1}{10}+\frac{1}{10}-\frac{1}{15}+\frac{1}{15}-\frac{1}{20}+...+\frac{1}{2005}-\frac{1}{2010}\right)\)

\(\Leftrightarrow N=\frac{1}{5}\left(1-\frac{1}{2010}\right)\)

\(\Leftrightarrow N=\frac{1}{5}.\frac{2009}{2010}=\frac{2009}{10050}\)

Bài 1:

a)\(\frac{2\cdot x-4,36}{0,125}=0,25\cdot42,9-11,7\cdot0,25+0,25\cdot0,8\)

\(\frac{2\cdot x-4,36}{0,125}=0,25\cdot\left(42,9-11,7+0,8\right)\)

\(\frac{2\cdot x-4,36}{0,125}=0,25\cdot32\)

\(\frac{2\cdot x-4,36}{0,125}=8\)

\(2\cdot x-4,36=8\cdot0,125\)

\(2\cdot x-4,36=1\)

\(2\cdot x=1+4,36\)

\(2\cdot x=5,36\)

\(x=\frac{5,36}{2}=2,68\)

b) \(N=\frac{1}{1\cdot5}+\frac{1}{5\cdot10}+\frac{1}{10\cdot15}+\frac{1}{15\cdot20}+...+\frac{1}{2005\cdot2010}\)

\(4N=\frac{4}{1\cdot5}+\frac{4}{5\cdot10}+\frac{4}{10\cdot15}+\frac{4}{15\cdot20}+...+\frac{4}{2005\cdot2010}\)

\(4N=1-\frac{1}{5}+\frac{1}{5}-\frac{1}{10}+\frac{1}{10}-\frac{1}{15}+\frac{1}{15}-\frac{1}{20}+...+\frac{1}{2005}-\frac{1}{2010}\)

\(4N=1-\frac{1}{2010}=\frac{2009}{2010}\)

\(N=\frac{2009}{2010}\div4=\frac{2009}{8040}\)

Bài 2:

a) ( x + 5,2 ) : 3,2 = 4,7 ( dư 0,5 )

\(x+5,2=4,7\cdot3,2+0,5\)

\(x+5,2=15,54\)

\(x=15,54-5,2=10,34\)

b)\(A=\frac{4047991-2010\cdot2009}{4050000-2011\cdot2009}\)

\(A=\frac{4047991-2010\cdot2009}{4050000-2009-2010\cdot2009}\)

\(A=\frac{4047991-2010\cdot2009}{4047991-2010\cdot2009}=1\)

Bài 3:

a) \(104,5\cdot x-14,1\cdot x+9,6\cdot x=25\)

\(x\cdot\left(104,5-14,1+9,6\right)=25\)

\(x\cdot100=25\)

\(x=\frac{25}{100}=\frac{1}{4}=0,25\)

b) \(T=\frac{2009\cdot2010+2000}{2011\cdot2010-2020}\)

\(T=\frac{2009\cdot2010+2000}{2009\cdot2010+4020-2020}\)

\(T=\frac{2009\cdot2010+2000}{2009\cdot2010+2000}=1\)

30 tháng 7 2015

\(N=\frac{1}{1.5}+\frac{1}{5.10}+\frac{1}{10.15}+\frac{1}{15.20}+...+\frac{1}{2005.2010}\)

\(N=\frac{1}{5}.\left(1-\frac{1}{5}+\frac{1}{5}-\frac{1}{10}+\frac{1}{10}-\frac{1}{15}+\frac{1}{15}-\frac{1}{20}+...+\frac{1}{2005}-\frac{1}{2010}\right)\)

\(N=\frac{1}{5}.\left(1-\frac{1}{2010}\right)\)

\(N=\frac{1}{5}.\frac{2009}{2010}\)

\(N=\frac{2009}{10050}\)

1 tháng 8 2018

\(=\frac{219}{520}=\frac{155052}{368160}\)

\(=\frac{303}{708}=\frac{157560}{368160}\)

\(\frac{155052}{368160}< \frac{157560}{368160}\)

VẬY \(\frac{303}{708}\)LỚN HƠN

26 tháng 7 2015

\(\frac{1\cdot3\cdot5+2\cdot6\cdot10+3\cdot9\cdot15}{3\cdot5\cdot12+6\cdot10\cdot24+9\cdot15\cdot36}=\frac{1+1+1}{12+12+12}=\frac{3\cdot1}{3\cdot12}=\frac{1}{12}\)

9 tháng 5 2019

\(\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{9}-\frac{1}{10}\right)\cdot10-x=10\)10

\(\left(1-\frac{1}{10}\right)\cdot10-10=x\)

\(x=10\cdot\left(1-\frac{1}{10}-1\right)\)

\(x=10\cdot-\frac{1}{10}=-1\)

9 tháng 5 2019

\(\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{9.10}\right).10-x=10\)

\(\left[1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{10}\right].10-x=10\)

\(\left[1+\left(\frac{1}{2}-\frac{1}{2}\right)+\left(\frac{1}{3}-\frac{1}{3}\right)+...+\left(\frac{1}{9}-\frac{1}{9}\right)-\frac{1}{10}\right].10-x=10\)

\(\left[1-\frac{1}{10}\right].10-x=10\)

\(\frac{9}{10}.10-x=10\)

\(9-x=10\)

\(x=9-10\)

\(x=-1\)

~ Hok tốt ~

22 tháng 6 2017

a)\(\frac{13}{15}+\frac{13}{35}+\frac{13}{63}+\frac{13}{99}\)

\(=\frac{13}{3.5}+\frac{13}{5.7}+\frac{13}{7.9}+\frac{13}{9.11}\)

\(=\frac{13}{2}\left(\frac{1}{3}-\frac{1}{5}+.....+\frac{1}{9}-\frac{1}{11}\right)\)

\(=\frac{13}{2}\left(\frac{1}{3}-\frac{1}{11}\right)\)

\(=\frac{13}{2}\cdot\frac{8}{33}\)

\(=\frac{52}{33}\)

22 tháng 6 2017

a) Đặt A= 13/15 + 13/35 + 13/63 + 13/99

A = 13/2 ( 2/15 + 2/35 + 2/63 + 2/99)

A= 13/2 ( 2/ 3.5 + 2/5.7 + 2/7.9 + 2/9.11)

A= 13/2 ( 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11)

A= 13/2 ( 1/3 - 1/11) 

A= 13/2 . 8/33

A= 52/33  

5 tháng 9 2017

a)\(\frac{25.4-0,5\cdot40\cdot0,2\cdot20\cdot0,25}{1+2+8+...+129+156}\)

\(=\frac{100-100}{1+2+8+...+156}\)

\(=\frac{0}{1+2+8+...+156}\)

\(=0\)

b)\(\frac{0,5\cdot40-0,5\cdot20\cdot8\cdot0,1\cdot0,25\cdot10}{128:8.16.4\left(4+52:4\right)}=\frac{20-20}{128:8.16.4.\left(4+52:4\right)}=\frac{0}{128:8.16.4.\left(4+52:4\right)}=0\)