$\text{Bài 1:}$

$\text{a) $\dfrac{6}{15}$ = $\dfrac{6 : 3}{15 : 3}$ = $\dfrac{2}{5}$}$

$\text{$\dfrac{9}{36}$ = $\dfrac{9 : 9}{36 : 9}$ = $\dfrac{1}{4}$}$

$\text{$\dfrac{77}{88}$ = $\dfrac{77 : 11}{88 : 11}$ = $\dfrac{7}{8}$}$

$\text{$\dfrac{15}{85}$ = $\dfrac{15 : 5}{85 : 5}$ = $\dfrac{3}{17}$}$

$\text{$\dfrac{16}{48}$ = $\dfrac{16 : 16}{48 : 16}$ = $\dfrac{1}{3}$}$

$\text{$\dfrac{21}{63}$ = $\dfrac{21 : 21}{63 : 21}$ = $\dfrac{1}{3}$}$

$\text{$\dfrac{37}{111}$ = $\dfrac{37 : 37}{111 : 37}$ = $\dfrac{1}{3}$}$

$\text{b) $\dfrac{666}{999}$ = $\dfrac{666 : 333}{999 : 333}$ = $\dfrac{2}{3}$}$

$\text{$\dfrac{4000}{6000}$ = $\dfrac{4000 : 2000}{6000 : 2000}$ = $\dfrac{2}{3}$}$

$\text{$\dfrac{500}{1000}$ = $\dfrac{500 : 500}{1000 : 500}$ = $\dfrac{1}{2}$}$

$\text{$\dfrac{15}{1515}$ = $\dfrac{15 : 15}{1515 : 15}$ = $\dfrac{1}{101}$}$

$\text{$\dfrac{201201}{119119}$ = $\dfrac{201201 : 1001}{119119 : 1001}$ = $\dfrac{201}{119}$}$

$\text{Bài 2:}$

$\text{a) Các phân số tối giản là:}$

$\text{$\dfrac{4}{9}$; $\dfrac{17}{13}$}$

$\text{b) $\dfrac{12}{21}$ = $\dfrac{12 : 3}{21 : 3}$ = $\dfrac{4}{7}$}$

$\text{$\dfrac{36}{63}$ = $\dfrac{36 : 9}{63 : 9}$ = $\dfrac{4}{7}$}$

$\text{$\dfrac{48}{84}$ = $\dfrac{48 : 12}{84 : 12}$ = $\dfrac{4}{7}$}$

$\text{$\dfrac{56}{24}$ = $\dfrac{56 : 8}{24 : 8}$ = $\dfrac{7}{3}$}$

$\text{Bài 3:}$

$\text{Ta có:}$

$\text{$\dfrac{10}{25}$ = $\dfrac{10 : 5}{25 : 5}$ = $\dfrac{2}{5}$}$

$\text{$\dfrac{14}{18}$ = $\dfrac{14 : 2}{18 : 2}$ = $\dfrac{7}{9}$}$

$\text{$\dfrac{15}{20}$ = $\dfrac{15 : 5}{20 : 5}$ = $\dfrac{3}{4}$}$

$\text{$\dfrac{16}{40}$ = $\dfrac{16 : 8}{40 : 8}$ = $\dfrac{2}{5}$}$

$\text{$\dfrac{36}{48}$ = $\dfrac{36 : 12}{48 : 12}$ = $\dfrac{3}{4}$}$

$\text{$\dfrac{63}{81}$ = $\dfrac{63 : 9}{81 : 9}$ = $\dfrac{7}{9}$}$

$\text{Vậy ta được các cặp phân số bằng nhau là:}$

$\text{1, $\dfrac{10}{25}$ và $\dfrac{16}{40}$}$

$\text{2, $\dfrac{14}{18}$ và $\dfrac{63}{81}$}$

$\text{3, $\dfrac{15}{20}$ và $\dfrac{36}{48}$}$

$\text{Bài 4:}$

$\text{a) Các phân số tối giản là:}$

$\text{$\dfrac{4}{9}$; $\dfrac{17}{13}$}$

$\text{b) Ta có:}$

$\text{$\dfrac{12}{21}$ = $\dfrac{12 : 3}{21 : 3}$ = $\dfrac{4}{7}$}$

$\text{$\dfrac{36}{63}$ = $\dfrac{36 : 9}{63 : 9}$ = $\dfrac{4}{7}$}$

$\text{$\dfrac{48}{84}$ = $\dfrac{48 : 12}{84 : 12}$ = $\dfrac{4}{7}$}$

$\text{$\dfrac{56}{24}$ = $\dfrac{56 : 8}{24 : 8}$ = $\dfrac{7}{3}$}$

$\text{$\dfrac{33}{77}$ = $\dfrac{33 : 11}{77 : 11}$ = $\dfrac{3}{7}$}$

$\text{Vậy các phân số bằng phân số $\dfrac{4}{7}$ là:}$

$\text{- $\dfrac{12}{21}$; $\dfrac{36}{63}$; $\dfrac{48}{84}$.}$

$\text{Chúc bạn học tốt nha!}$

`@Lynh`

Đáp án:

Kéo xuống dưới xem cách làm nhe em :he: 

Có gì khumm hiểu bảo chị nhee ^^

𝙷𝚊𝚎◍•ᴗ•◍

Giải thích các bước giải:

Bài `1:`

`a) 6/15 = {6:3}/{15:3}=2/5`

`9/36={9:9}/{36:9}=1/4`

`77/88={77:11}/{88:11}=7/8`

`15/85={15:5}/{85:5}=3/17`

`16/48={16:16}/{48:16}=1/3`

`9/36={9:9}/{36:9}=1/4`

`21/63={21:21}/{63:21}=1/3`

`37/111={37:37}/{111:37}=1/3`

`b) 666/999={666:333}/{999:333}=2/3`

`4000/6000={4000:2000}/{6000:2000}=2/3`

`500/1000={500:500}/{1000:500}=1/2`

`15/1515={15:15}/{1515:15}=1/101`

`201201/119119={201201:1001}/{119119:1001}=201/119`

Bài `2:`

`a)` Các phân số tối giản: `4/9` và `17/13.`

`b) 12/21={12:3}/{21:3}=4/7`

`36/63={36:9}/{63:9}=4/7`

`48/84={48:12}/{84:12}=4/7`

`56/24={56:8}/{24:8}=7/3`

Bài `3:`

`10/25={10:5}/{25:5}=2/5`

`14/18={14:2}/{18:2}=7/9`

`15/20={15:5}/{20:5}=3/4`

`16/40={16:8}/{40:8}=2/5`

`36/48={36:12}/{48:12}=3/4`

`63/81={63:9}/{81:9}=7/9`

Vậy các phân số bằng nhau : `10/25=16/40;14/18=63/81; 15/20=36/48`

Bài `4:`

`a)` Các phân số tối giản: `4/9` và `17/13.`

`b) 12/21={12:3}/{21:3}=4/7`

`36/63={36:9}/{63:9}=4/7`

`48/84={48:12}/{84:12}=4/7`

`56/24={56:8}/{24:8}=7/3`

`33/77={33:11}/{77:11}=3/7`

Vậy các phân số bằng `4/7: 36/63;12/21;48/84`

`*`Tự nhinn thấy mìn làm tốn mất mấy tiếng thankxuan $;-;$

$Hae2k9$