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vì 1/2<1=> -1/2>-1(âm ngược lại vs dương)
1,7>0 mà -1,7<0=> 1,7>-1,7
vì -1/2<0/2=0 => -1/2<0
a,Ta thấy \(-\frac{2}{2}< -\frac{1}{2}\Rightarrow-1< \frac{-1}{2}\)
b,Vì \(1,7>0;-1.7< 0\Rightarrow-1,7< 1,7\)
c,Vì \(-\frac{1}{2}< 0\)
Vậy....
1.
a, Ta có : \(-3\dfrac{1}{9}=\dfrac{-28}{9}\\ -3\dfrac{2}{9}=\dfrac{-29}{9}\)
Vì -28 > -29 mà 9 > 0
Nên \(\dfrac{-28}{9}>\dfrac{-29}{9}hay-3\dfrac{1}{9}>-3\dfrac{2}{9}\)
b, Ta có: 12 < 21
Nên: -4,12 < -4,21
c, Ta có: 3 > 03
Nên: -7,3 > -7,03
2. Sắp xếp:
, \(a,-\dfrac{1}{2};0;\dfrac{1}{2}\\ b,-1,7;0;1,7\\ c,-2,1;0,5;2,5\\ d,-1\dfrac{2}{3};\dfrac{-5}{6};0;0,7\)
1)mik ko biết trục số ở đâu nên tham khảo:
2
-0,75 <5/3
a) \(\frac{1}{8}>0>\frac{-3}{8}=>\frac{1}{8}>\frac{-3}{8}\)
b) \(\frac{-3}{7}< 0< 2\frac{1}{2}=>\frac{-3}{7}< 2\frac{1}{2}\)
c) \(-3.9< 0< 0.1=>-3.9< 0.1\)
d) \(-2.3< 0< 3.2=>-2.3< 3.2\)
\(a,\dfrac{a}{b}>1\Leftrightarrow a>1\cdot b=b\\ \dfrac{a}{b}< 1\Leftrightarrow a< 1\cdot b=b\\ b,\dfrac{a}{b}=\dfrac{a\left(b+1\right)}{b\left(b+1\right)}=\dfrac{ab+a}{b^2+b}\\ \dfrac{a+1}{b+1}=\dfrac{b\left(a+1\right)}{b\left(b+1\right)}=\dfrac{ab+b}{b^2+b}\\ \forall a=b\Leftrightarrow\dfrac{a}{b}=\dfrac{a+1}{b+1}\\ \forall a>b\Leftrightarrow\dfrac{a}{b}>\dfrac{a+1}{b+1}\\ \forall a< b\Leftrightarrow\dfrac{a}{b}< \dfrac{a+1}{b+1}\)
\(c,\forall a>b\Leftrightarrow\dfrac{a}{b}-1=\dfrac{a-b}{b}>\dfrac{a-b}{b+n}\left(b< b+n;a-b>0\right)=\dfrac{a+n}{b+n}-1\\ \Leftrightarrow\dfrac{a}{b}>\dfrac{a+n}{b+n}\\ \forall a< b\Leftrightarrow1-\dfrac{a}{b}=\dfrac{b-a}{b}>\dfrac{b-a}{b+n}\left(b< b+n;b-a>0\right)=1-\dfrac{a+n}{b+n}\\ \Leftrightarrow1-\dfrac{a}{b}>1-\dfrac{a+n}{b+n}\Leftrightarrow\dfrac{a}{b}>\dfrac{a+n}{b+n}\\ \forall a=b\Leftrightarrow\dfrac{a+n}{b+n}=\dfrac{a}{b}\left(=1\right)\)
Câu 1 :
\(\dfrac{-25}{37}\&\dfrac{-20}{31}\)
Ta thấy \(\dfrac{-25}{37}< \dfrac{-20}{37}\)
mà \(\dfrac{-20}{37}< \dfrac{-20}{31}\)
\(\Rightarrow\dfrac{-25}{37}< \dfrac{-20}{31}\)
Câu 2 :
\(\dfrac{2}{3}\&\dfrac{5}{7}\)
\(\dfrac{2}{3}:\dfrac{5}{7}=\dfrac{2}{3}.\dfrac{7}{5}=\dfrac{14}{15}< 1\)
\(\Rightarrow\dfrac{5}{7}>\dfrac{2}{3}\) Câu 3 : \(\dfrac{8}{13}\&\dfrac{5}{7}\)Ta thấy \(\dfrac{8}{13}:\dfrac{5}{7}=\dfrac{8}{13}.\dfrac{7}{5}=\dfrac{56}{65}< 1\)
\(\Rightarrow\dfrac{8}{13}< \dfrac{5}{7}\)
Lời giải:
a. $\frac{3}{-7}=\frac{-27}{63}$
$\frac{-5}{9}=\frac{-35}{63}$
Do $\frac{27}{63}< \frac{35}{63}$ nên $\frac{-27}{63}> \frac{-35}{63}$
$\Rightarrow \frac{3}{-7}> \frac{-5}{9}$
---------
b.
$-0,625=\frac{-625}{1000}=\frac{-5}{8}=\frac{-125}{200}$
$\frac{-19}{50}=\frac{-76}{200}> \frac{-125}{200}$
$\Rightarrow -0,625> \frac{-19}{50}$
c.
$-2\frac{5}{9}=-(2+\frac{5}{9})=\frac{-23}{9}=-(\frac{-23}{-9})$
Bài 1 rất dễ nên bạn tự làm nhé
Bài 2:
a) \(\left|x-1,7\right|=2,3\)
\(\Rightarrow x-1,7=\pm2,3\)
+) \(x-1,7=2,3\Rightarrow x=4\)
+) \(x-1,7=-2,3\Rightarrow x=-0,6\)
Vậy x = 4 hoặc x = -0,6
b) \(\left|x+\frac{3}{4}\right|-\frac{1}{3}=0\)
\(\Rightarrow\left|x+\frac{3}{4}\right|=\frac{1}{3}\)
\(\Rightarrow x+\frac{3}{4}=\pm\frac{1}{3}\)
+) \(x+\frac{3}{4}=\frac{1}{3}\Rightarrow x=\frac{-5}{12}\)
+) \(x+\frac{3}{4}=-\frac{1}{3}\Rightarrow x=\frac{-13}{12}\)
Vậy \(x=\frac{-5}{12}\) hoặc \(x=\frac{-13}{12}\)
a: -3/100=-9/300; -2/3=-200/300
=>-3/100>-2/3
b: -3/5=-9/15
-2/3=-10/15
=>-3/5>-2/3
c: -5/4<-1<-3/8
d: -2/3=-8/12; -3/4=-9/12
=>-2/3>-3/4
e: -267/268>-1
-1>-1347/1343
=>-267/268>-1347/1343
So sánh
\(-\dfrac{1}{2}\) và \(-1\)
\(-\dfrac{1}{2}=-0,5\)
\(\Rightarrow-0,5>-1\)
\(\Rightarrow-\dfrac{1}{2}>-1\)
\(1,7>-1,7\)
\(-\dfrac{1}{2}< 0\)