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a) Ta có:
\(-\dfrac{24}{35}< -\dfrac{24}{30}< -\dfrac{19}{30}\)
\(\Rightarrow x< y\)
b) Ta có:
\(A=\dfrac{2006}{2007}-\dfrac{2007}{2008}+\dfrac{2008}{2009}-\dfrac{2009}{2010}\)
\(A=\left(1-\dfrac{1}{2007}\right)-\left(1-\dfrac{1}{2008}\right)+\left(1-\dfrac{1}{2009}\right)-\left(1-\dfrac{1}{2010}\right)\)
\(A=1-\dfrac{1}{2007}-1+\dfrac{1}{2008}+1-\dfrac{1}{2009}-1+\dfrac{1}{2010}\)
\(A=-\dfrac{1}{2007}+\dfrac{1}{2008}-\dfrac{1}{2009}+\dfrac{1}{2010}\)
Ta lại có:
\(B=-\dfrac{1}{2006.2007}-\dfrac{1}{2008.2009}\)
\(B=-\dfrac{1}{2006}+\dfrac{1}{2007}-\dfrac{1}{2008}+\dfrac{1}{2009}\)
=> Dễ dàng thấy A > B
a.
Ta có:\(\frac{-45}{47}>-1\) và \(\frac{51}{-50}< -1\)\(\Rightarrow\)\(\frac{-45}{47}>\frac{51}{-50}\Rightarrow x>y\)
b.
x>y mà
a/
\(x-y=\frac{a}{b}-\frac{c}{d}=\frac{ad-cb}{bd}=\frac{1}{bd}.\) (1)
\(y-z=\frac{c}{d}-\frac{e}{h}=\frac{ch-de}{dh}=\frac{1}{dh}\)(2)
+ Nếu d>0 => (1)>0 và (2)>0 => x>y; y>x => x>y>z
+ Nếu d<0 => (1)<0 và (2)<0 => x<y; y<z => x<y<z
b/
\(m-y=\frac{a+e}{b+h}-\frac{c}{d}=\frac{ad+de-cb-ch}{d\left(b+h\right)}=\frac{\left(ad-cb\right)-\left(ch-de\right)}{d\left(b+h\right)}=\frac{1-1}{d\left(b+h\right)}=0\)
=> m=y
+
cảm ơn bn nha Nguyễn Ngoc Anh Minh mk k cho bn r đó kb vs mk nha
Ta có: \(\dfrac{a}{b}\) và \(\dfrac{c}{d}\left(b>0,d>0\right)\)
a) Giả sử: +) \(\dfrac{a}{b}=\dfrac{c}{d}\) \(\Rightarrow\) \(ad=bc\) (nhân chéo)
\(\Rightarrow\) nếu \(\dfrac{a}{b}< \dfrac{c}{d}\) thì \(ad< bc.\)
b) Giả sử \(ad=bc\) \(\Rightarrow\dfrac{a}{b}=\dfrac{c}{d}\)
\(\Rightarrow\) nếu \(ad< bc\) thì \(\dfrac{a}{b}< \dfrac{c}{d}.\)
-1/540<0<1/3780
\(\dfrac{-2003}{2004}>-1>-\dfrac{2005}{2003}\)
\(\frac{2008}{2009};\frac{20}{19}\)
\(1-\frac{2008}{2009}=\frac{1}{2009}\)
\(1-\frac{20}{19}=\frac{-1}{19}=\frac{1}{19}\)
Vì 19 < 2009 Nên \(\frac{1}{2009}< \frac{1}{19}\)
Vậy \(\frac{2008}{2009}>\frac{20}{19}\)
1.\(\frac{1001}{1000}>\frac{1000}{1000}=1=\frac{1003}{1003}>\frac{1002}{1003}\Rightarrow\frac{1001}{1000}>\frac{1002}{1003}\)
2.a) \(x=\frac{a-3}{2a}\left(a\ne0\right)\)
\(=\frac{1}{2}\left(1-\frac{3}{a}\right)\inℤ\)
\(\Leftrightarrow\hept{\begin{cases}1-\frac{3}{a}\inℤ\\1-\frac{3}{a}⋮2\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}\frac{3}{a}\inℤ\\\frac{3}{a}\equiv1\left(mod2\right)\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}a\inƯ\left(3\right)=\left\{\pm1;\pm3\right\}\\\frac{3}{a}\equiv1\left(mod2\right)\end{cases}}\)
Ta có bảng :
| \(a\) | \(1\) | \(-1\) | \(3\) | \(-3\) |
| \(\frac{3}{a}\) | \(3\) | \(-3\) | \(1\) | \(-1\) |
| \(1-\frac{3}{a}\) | \(-2\) | \(4\) | \(0\) | \(2\) |
| \(x\) | \(-1\) | \(2\) | \(0\) | \(1\) |
Vậy \(a\in\left\{\pm1;\pm3\right\}\)
b)Ta có:\(\frac{a+2009}{a-2009}=1+\frac{4018}{a-2009}\left(a\ne2009\right)\)
\(\frac{b+2010}{b-2010}=1+\frac{4020}{b-2010}\left(b\ne2010\right)\)
\(\Rightarrow\frac{4018}{a-2009}=\frac{4020}{b-2010}\)
\(\Rightarrow\frac{a-2009}{4018}=\frac{b-2010}{4020}\)
\(\Rightarrow\frac{a-2009}{2009}=\frac{b-2010}{2010}\)
\(\Rightarrow\frac{a}{2009}-1=\frac{b}{2010}-1\)
\(\Rightarrow\frac{a}{2009}=\frac{b}{2010}\)
\(\dfrac{2009}{2010}=\dfrac{2009\cdot10001}{2010\cdot10001}=\dfrac{20092009}{20102010}\)
\(\dfrac{2009}{2010}=\dfrac{20092009}{20102010}\)