a) Ta có :
\(\frac{18}{91}< \frac{18}{90}=\frac{1}{5}=\frac{23}{115}< \frac{23}{114}\)
\(\Rightarrow\frac{18}{91}< \frac{23}{114}\)
b) Ta có :
\(\frac{21}{52}=\frac{210}{520}=1-\frac{310}{520}\)
\(\frac{213}{523}=1-\frac{310}{523}\)
Mà \(1-\frac{310}{520}< 1-\frac{310}{523}\)
\(\Rightarrow\frac{21}{52}< \frac{213}{523}\)
c) Ta có : \(\frac{1313}{9191}=\frac{13}{91}=\frac{1}{7}=\frac{11}{77};\frac{1111}{7373}=\frac{11}{73}\)
Mà \(\frac{11}{77}< \frac{11}{73}\)nên \(\frac{1313}{9191}< \frac{1111}{7373}\)
d) Ta có :
\(\frac{n}{n+1}=\frac{n+1-1}{n+1}=1-\frac{1}{n+1}\)
\(\frac{n+2}{n+3}=\frac{n+3-1}{n+3}=1-\frac{1}{n+3}\)
Mà \(1-\frac{1}{n+1}< 1-\frac{1}{n+3}\)nên \(\frac{n}{n+1}< \frac{n+2}{n+3}\)
a) Ta có : \(\frac{18}{91}< \frac{18}{90}=\frac{1}{5}< \frac{23}{115}< \frac{23}{114}\)
\(\Rightarrow\) \(\frac{18}{91}< \frac{23}{114}\)
Vậy \(\frac{18}{91}< \frac{23}{114}\)
b) Ta có : \(\frac{21}{52}< \frac{21}{56}=\frac{3}{8}< \frac{213}{568}< \frac{213}{523}\)
\(\Rightarrow\) \(\frac{21}{52}< \frac{213}{523}\)
Vậy \(\frac{21}{52}< \frac{213}{523}\)
c) Ta có : \(\frac{1313}{9191}=\frac{1313:1313}{9191:1313}=\frac{1}{7}\)
\(\frac{1111}{7373}=\frac{1111:101}{7373:101}=\frac{11}{73}\)
Lại có : \(\frac{1}{7}< \frac{11}{77}< \frac{11}{73}\)
\(\Rightarrow\) \(\frac{1313}{9191}< \frac{1111}{7373}\)
Vậy \(\frac{1313}{9191}< \frac{1111}{7373}\)
d) Ta có : \(1-\frac{n}{n+1}=\frac{n+1}{n+1}-\frac{n}{n+1}=\frac{1}{n+1}\)
\(1-\frac{n+2}{n+3}=\frac{n+3}{n+3}-\frac{n+2}{n+3}=\frac{1}{n+3}\)
Vì \(n+1< n+3\)
\(\Rightarrow\)\(\frac{1}{n+1}>\frac{1}{n+3}\)
\(\Rightarrow\) \(\frac{n}{n+1}< \frac{n+2}{n+3}\)
Vậy \(\frac{n}{n+1}< \frac{n+2}{n+3}\)
Chúc m.n hok tốt ♡❤️
P/s :
a)
Ta có : \(\frac{18}{91}< \frac{18}{90}=\frac{1}{5}< \frac{23}{115}< \frac{23}{114}\)
\(\Rightarrow\) \(\frac{18}{91}< \frac{23}{114}\)
Vậy \(\frac{18}{91}< \frac{23}{114}\)
b)
Ta có : \(\frac{21}{52}< \frac{21}{56}=\frac{3}{8}< \frac{213}{568}< \frac{213}{523}\)
\(\Rightarrow\) \(\frac{21}{52}< \frac{213}{523}\)
Vậy \(\frac{21}{52}< \frac{213}{523}\)
c)
Ta có : \(\frac{1313}{9191}=\frac{1313:1313}{9191:1313}=\frac{1}{7}\)
\(\frac{1111}{7373}=\frac{1111:101}{7373:101}=\frac{11}{73}\)
Lại có : \(\frac{1}{7}< \frac{11}{77}< \frac{11}{73}\)
\(\Rightarrow\) \(\frac{1313}{9191}< \frac{1111}{7373}\)
Vậy \(\frac{1313}{9191}< \frac{1111}{7373}\)
d )
Ta có :
\(\frac{n}{n+1}=\frac{n+1-1}{n+1}=1-\frac{1}{n+1}\)
\(\frac{n+2}{n+3}=\frac{n+3-1}{n+3}=1-\frac{1}{n+3}\)
Do \(\frac{1}{n+1}>\frac{1}{n+3}\left(n+1< n+3\right)\)
\(\Rightarrow1-\frac{1}{n+1}>1-\frac{1}{n+3}\)
\(\Rightarrow\frac{n}{n+1}>\frac{n+2}{n+3}\)
Vậy ...
~ Ủng hộ nha
