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n/n+2 > n/n+9 > n-2/n+9
=> n/n+2 > n-2/n+9
K mk nha,mk âm điểm rùi!huhu
n-2<n+9\(\Rightarrow\)\(\frac{n-2}{n+9}<\frac{n}{n+11}<\frac{n}{n+2}\)
Vậy \(\frac{n}{n+2}>\frac{n-2}{n+9}\)
Ta số phân số chung gian là \(\frac{n+1}{n+3}\)
Vì \(\frac{n}{n+3}< \frac{n+1}{n+3}< \frac{n+1}{n+2}\)
Nên \(\frac{n}{n+3}< \frac{n+1}{n+2}\)
Ủng hộ nhé !
Ta có: \(\frac{n-2}{n+9}=\frac{n}{n+9}-\frac{2}{n+9}\)(n thuộc N*). Vì \(\frac{n}{n+8}>\frac{n}{n+9}\)nên \(\frac{n}{n+8}>\frac{n}{n+9}>\frac{n}{n+9}-\frac{2}{n+9}\)
a) \(\frac{5}{9}=\frac{20}{36};\frac{1}{4}=\frac{9}{36}\)
\(\frac{20}{36}>\frac{9}{36}\Rightarrow\frac{5}{9}>\frac{1}{4}\)
\(\frac{72}{73}=\frac{4248}{4307};\frac{58}{59}=\frac{4234}{4307}\)
\(\frac{4248}{4307}>\frac{4234}{4307}\Rightarrow\frac{72}{73}>\frac{58}{59}\)
\(\frac{n}{n+3}=\frac{n+1}{n-1}=\frac{n+1}{3-2}=\frac{n+1}{n+2}\)
\(\Rightarrow\frac{n}{n+3}=\frac{n+1}{n+2}\)
Ta có :
\(\frac{n-2}{n+9}=\frac{n}{2+9}-\frac{2}{2+9}\)\(\left(n\in N\text{*}\right)\)
Vì \(\frac{n}{n+8}>\frac{n}{n+9}\)
\(\Rightarrow\frac{n}{n+8}>\frac{n}{n+9}>\frac{n}{n+9}-\frac{2}{n+9}\)
\(\Leftrightarrow\frac{n}{n+8}>\frac{n}{n+9}>\frac{n-2}{n+9}\)
\(\frac{\Rightarrow n}{n+8}>\frac{n-2}{n+9}\)
h) Ta có: \(\frac{n+1}{n+2}=1-\frac{1}{n+2}\)
\(\frac{n+3}{n+4}=\frac{1}{n+4}\)
Vì \(n+2< n+4\)\(\Rightarrow\frac{1}{n+2}>\frac{1}{n+4}\)
\(\Rightarrow1-\frac{1}{n+2}< 1-\frac{1}{n+4}\)\(\Rightarrow\frac{n+1}{n+2}< \frac{n+3}{n+4}\)
Vì n/n+8 > n/n+9 > n-2/n+9
=> n/n + 8 > n - 2/n+9
k mk nha,mk âm điểm rùi!huhu