Bài 6: So sánh phân số

Lời giải:
a.

\(A-B=\frac{20-14}{39}+(\frac{22}{27}-\frac{22}{29})+(\frac{18}{43}-\frac{18}{41})\)

\(=\frac{6}{39}+22.\frac{2}{27.29}+\frac{18.(-2)}{43.41}=\frac{6}{39}+\frac{44}{27.29}-\frac{36}{43.41}\)

Dễ thấy $\frac{44}{27.29}> \frac{36}{43.41}; \frac{6}{39}>0$ nên $A-B>0$

$\Rightarrow A>B$

b.

\(A-B=\frac{3-7}{8^3}+\frac{7-3}{8^4}=\frac{4}{8^4}-\frac{4}{8^3}=\frac{4(8^3-8^4)}{8^3.8^4}<0\Rightarrow A< B\)

c.

\(A-1=\frac{13}{10^7-8}; B-1=\frac{13}{10^8-7}\)

Mà \(10^7-8-(10^8-7)=10^7-10^8-1<0\Rightarrow 10^7-8< 10^8-7\Rightarrow A-1> B-1\)

$\Rightarrow A>B$

d.

\(A=\frac{10^{1992}+1}{10^{1991}+1}>\frac{10^{1991}+1}{10^{1991}+1}=1; B=\frac{10^{1993}+1}{10^{1994}+1}<\frac{10^{1993}+1}{10^{1993}+1}=1\)

$\Rightarrow A>B$

a) 5/-6 < 5/-7    b) -12/15 < 1/5   c) -3/8 > -5/6   d)   -14/21 < 60/-72

a)5/-6>5/-7 nhé vì tử = nhau mà -6>-7

b)-12/15 và 3/5=>3>-12=>-12/15<3/5

c)-3/8>-5/6

d)-14/21>-60/72 nhé

-4/5=-20/25

-4/5=-20/25 vì -4x25 = -20 x 5

15/10 hay 3/2 nhé

\(1,5=\dfrac{15}{10}=\dfrac{3}{2}\)

\(=\dfrac{3}{2};\dfrac{15}{10};\dfrac{20}{15};......\)

helpppppppppppp

-17/10

mng ơi giúp e với ạ

cần gấppppppppppppppppppp

chệu lun á khó quấ

giúp mình

\(-\dfrac{10}{6}< -\dfrac{3}{2}< -\dfrac{7}{6}\)

\(\dfrac{-3}{2}\)

a: \(\dfrac{-10}{6}< \dfrac{x}{2}< -\dfrac{7}{6}\)

\(\Leftrightarrow\dfrac{-10}{6}< \dfrac{3x}{6}< \dfrac{-7}{6}\)

=>3x=-9(vì x là số nguyên)

hay x=-3

b: \(\dfrac{-3}{4}< \dfrac{x}{6}< \dfrac{-1}{2}\)

\(\Leftrightarrow\dfrac{-9}{12}< \dfrac{2x}{12}< \dfrac{-6}{12}\)

\(\Leftrightarrow2x=-8\)

hay x=-4

c: \(\Leftrightarrow\dfrac{-12}{27}< \dfrac{-12}{4x}< \dfrac{-12}{30}\)

=>4x=28

hay x=7

giải chi tiết cho mik ạ