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ai tk mình mình tk lại cho!!!
a) \(\dfrac{6}{13}:\left(\dfrac{1}{2}-x\right)=\dfrac{15}{39}\)
\(\dfrac{1}{2}-x=\dfrac{6}{13}:\dfrac{15}{39}\)
\(\dfrac{1}{2}-x=\dfrac{6}{5}\)
\(x=\dfrac{1}{2}-\dfrac{6}{5}\)
\(x=-\dfrac{7}{10}\)
b) \(3\times\left(\dfrac{x}{4}+\dfrac{x}{28}+\dfrac{x}{70}+\dfrac{x}{130}\right)=\dfrac{60}{13}\)
\(3\times x\times\left(\dfrac{1}{4}+\dfrac{1}{28}+\dfrac{1}{70}+\dfrac{1}{130}\right)=\dfrac{60}{13}\)
\(x\times\left(\dfrac{3}{1\times4}+\dfrac{3}{4\times7}+\dfrac{3}{7\times10}+\dfrac{3}{7\times13}\right)=\dfrac{60}{13}\)
\(x\times\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{13}\right)=\dfrac{60}{13}\)
\(x\times\left(1-\dfrac{1}{13}\right)=\dfrac{60}{13}\)
\(x\times\dfrac{12}{13}=\dfrac{60}{13}\)
\(x=\dfrac{60}{13}:\dfrac{12}{13}\)
\(x=5\)
Ta có: 12/13 = 1 - 1/13
13/14 = 1 - 1/14
Vì 1/13 > 1/14 nên 12/13 < 13/14
c; 17\(\dfrac{2}{31}\) - (\(\dfrac{15}{17}\) + 6\(\dfrac{2}{31}\))
= 17 + \(\dfrac{2}{31}\) - \(\dfrac{15}{17}\) - 6 - \(\dfrac{2}{31}\)
= (17 - 6) - \(\dfrac{15}{17}\) + (\(\dfrac{2}{31}\) - \(\dfrac{2}{31}\))
= 11 - \(\dfrac{15}{17}\)+ 0
= \(\dfrac{172}{17}\)
b; 130\(\dfrac{25}{28}\) + 120\(\dfrac{17}{35}\)
= 130 + \(\dfrac{25}{28}\) + 120 + \(\dfrac{17}{35}\)
= (130 + 120) + (\(\dfrac{25}{28}\) + \(\dfrac{17}{35}\))
= 250 + (\(\dfrac{125}{140}\) + \(\dfrac{68}{140}\))
= 250 + \(\dfrac{193}{140}\)
= 250\(\dfrac{193}{140}\)
(1) \(\frac{2002}{2003}\)và \(\frac{145}{146}\)
Ta có: \(1-\frac{2002}{2003}=\frac{1}{2003}\); \(1-\frac{145}{146}=\frac{1}{145}\)
Vì \(\frac{1}{2003}< \frac{1}{146}\Rightarrow-\frac{1}{2003}>-\frac{1}{146}\)
\(\Rightarrow1-\frac{1}{2003}>1-\frac{1}{146}\)\(\Rightarrow\frac{2002}{2003}>\frac{145}{146}\)
Vậy \(\frac{2002}{2003}>\frac{145}{146}\)
(2) \(\frac{2012}{2013}\)và \(\frac{2012}{2015}\)
Vì: \(2013< 2015\Rightarrow\frac{2012}{2013}>\frac{2012}{2015}\)
Vậy: \(\frac{2012}{2013}>\frac{2012}{2015}\)
(3) \(\frac{159}{163}\) và \(\frac{374}{371}\)
Vì \(\frac{159}{163}< 1\)và \(\frac{374}{371}>1\)
Nên \(\frac{374}{371}>\frac{159}{163}\)
Vậy \(\frac{374}{371}>\frac{159}{163}\)
(4) \(\frac{50}{110}\)và \(\frac{65}{120}\)
Ta có: \(\frac{50}{110}< \frac{50}{100}=\frac{1}{2}\) và \(\frac{65}{120}>\frac{60}{120}=\frac{1}{2}\)
\(\Rightarrow\frac{50}{110}< \frac{65}{120}\)
Vậy \(\frac{50}{110}< \frac{65}{120}\)
(5) \(\frac{127}{139}\)và \(\frac{130}{134}\)
Ta có: \(\frac{127}{139}< \frac{127}{134}< \frac{130}{134}\)
\(\Rightarrow\frac{127}{139}< \frac{130}{134}\)
Vậy \(\frac{127}{139}< \frac{130}{134}\)
\(2013< 2015\Rightarrow\frac{2012}{2013}>\frac{2012}{2015}\)\(2013< 2015\Rightarrow\frac{2012}{2013}>\frac{2012}{2015}\)