`40/35= 8/7`

`8=8->40/35=8/7`

a) 

\(\dfrac{6}{12}=\dfrac{6:6}{12:6}=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{1}{2}=\dfrac{1\times2}{2\times2}=\dfrac{2}{4}\)

Mà \(\dfrac{2}{4}< \dfrac{3}{4}\)

Vậy \(\dfrac{6}{12}< \dfrac{3}{4}\).

b)

\(\dfrac{8}{10}=\dfrac{8:2}{10:2}=\dfrac{4}{5}\)

Mà \(\dfrac{2}{5}< \dfrac{4}{5}\)

Vậy \(\dfrac{2}{5}< \dfrac{8}{10}\).

c)

\(\dfrac{40}{35}=\dfrac{40:5}{35:5}=\dfrac{8}{7}\)

Mà \(\dfrac{8}{7}>\dfrac{6}{7}\)

Vậy \(\dfrac{40}{35}>\dfrac{6}{7}\).

d)

\(\dfrac{8}{16}=\dfrac{8:8}{16:8}=\dfrac{1}{2}\)

Mà \(\dfrac{1}{2}< \dfrac{5}{2}\)

Vậy \(\dfrac{8}{16}< \dfrac{5}{2}\).

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Bài 2: So sánh các phân số sau

7/15 > 5/13              11/12 > 7/48        24/35 > 21/7           15/26 > 7/8

10/15= 10:5/15:5=2/3

7/35= 7:7/35:7= 1/3

Ta thấy: 2/3 > 1/3 (2 > 1)

Hay: 10/15 > 7/35

\(\frac{7}{35}\)= \(\frac{1}{5}\)\(\frac{10}{15}=\frac{2}{3}\)

\(\frac{2}{3}>\frac{1}{5}\) t i c k cho mình nha

Rút gọn: 

\(\frac{7}{35}\)= \(\frac{1}{5}\)

Quy đồng: MSC là 15

=> \(\frac{1}{5}=\frac{1x3}{5x3}=\frac{3}{15}\); giữ nguyên phân số \(\frac{10}{15}\)

So sánh:

\(\frac{10}{15}>\frac{3}{15}\)

=> \(\frac{10}{15}>\frac{7}{35}\)

Bài 1: 

a) \(\dfrac{-5}{6}\ne\dfrac{10}{-14}\left(\dfrac{10}{-14}=-\dfrac{5}{7}\right).\)

b) \(\dfrac{-15}{-60}\ne\dfrac{-3}{12}\left(\dfrac{-15}{-60}=\dfrac{1}{4}\right).\)

Bài 2:

a) \(\dfrac{20}{-140}=-\dfrac{1}{7}.\)

b) \(\dfrac{4.18}{9.12}=\dfrac{72}{108}=\dfrac{2}{3}.\)

c) \(\dfrac{17.25-17.3}{2.\left(-15\right)}=\dfrac{17.\left(25-3\right)}{-30}=-\dfrac{17.22}{30}=\dfrac{374}{30}=\dfrac{187}{15}.\)

Bài 3:

a) \(\dfrac{-3}{5}< \dfrac{4}{-7}.\)

b) \(\dfrac{-4}{21}>\dfrac{-7}{35}.\)

c) \(\dfrac{-7}{24}>\dfrac{-2}{3}.\)

d) \(\dfrac{-52}{167}< \dfrac{-3}{-4}.\)

\(\dfrac{90}{126}=\dfrac{5}{7}\)

\(\Rightarrow\dfrac{90}{126}< \dfrac{6}{7}\) (Vì \(\dfrac{5}{7}< \dfrac{6}{7}\))

\(\dfrac{35}{49}=\dfrac{5}{7}\)

\(\Rightarrow\dfrac{90}{126}=\dfrac{35}{49}\) (Vì \(\dfrac{5}{7}=\dfrac{5}{7}\))

\(\dfrac{90}{126}\) = \(\dfrac{90:18}{126:18}\) = \(\dfrac{5}{7}\) so sánh \(\dfrac{5}{7}< \dfrac{6}{7}\) nên \(\dfrac{90}{126}< \dfrac{6}{7}\)

\(\dfrac{90}{126}=\dfrac{5}{7}\) và \(\dfrac{35}{49}\) = \(\dfrac{35:7}{49:7}=\dfrac{5}{7}\) so sánh \(\dfrac{5}{7}=\dfrac{5}{7}\) nên \(\dfrac{90}{126}=\dfrac{35}{49}\)

a.Ta có:
\(\dfrac{14}{18}=\dfrac{7}{9}=\dfrac{7\times5}{9\times5}=\dfrac{35}{45}\)
\(\dfrac{21}{35}=\dfrac{3}{5}=\dfrac{3\times9}{5\times9}=\dfrac{27}{45}\)
\(\Rightarrow\dfrac{14}{18}>\dfrac{21}{35}\)

14/8 = 35/45 , 21/35 = 27/45

nên 14/18>21/35

(HT)

Bài 1:

\(\frac{90}{126}=\frac{5}{7};\frac{6}{7}=\frac{6}{7}\)

\(\frac{90}{126}=\frac{5}{7};\frac{35}{49}=\frac{5}{7}\)

Bài 2:

ta có: 8/9 = 0,8888

19/20 = 0,95

10/11 = 0,9090

21/22 = 0,9595

=> 21/22 là phân số lớn nhất

\(\frac{16}{48}=\frac{16:16}{48:16}=\frac{1}{3}\);\(\frac{14}{35}=\frac{14:7}{35:7}=\frac{2}{5}\)

\(\frac{1}{3}=\frac{1\cdot5}{3\cdot5}=\frac{5}{15}\);    \(\frac{2}{5}=\frac{2\cdot3}{5\cdot3}=\frac{6}{15}\)