-9/6; -5/6; -9/6

90/45; -90/45; -35/45

ta có 2/3 = 2x4/3x 4=8/12 và giữ nguyên phân số 5/12

vậy quy đồng 2 phân số 2/3 và 5/12 được 2 phân số 8/12 và 5/12

90/72 = 90:18/72:18 = 5/4

72/42 = 72:6/42:6 = 12/7

ídsdsdddđ

\(a.\dfrac{5}{10}=\dfrac{1}{2}=\dfrac{1\times3}{2\times3}=\dfrac{3}{6}\)

\(\dfrac{25}{75}=\dfrac{1}{3}=\dfrac{1\times2}{3\times2}=\dfrac{2}{6}\)

\(b.\dfrac{42}{56}=\dfrac{3}{4}=\dfrac{3\times2}{4\times2}=\dfrac{6}{8}\)

\(\dfrac{18}{48}=\dfrac{3}{8}\)

\(c.\dfrac{27}{81}=\dfrac{1}{3}=\dfrac{1\times4}{3\times4}=\dfrac{4}{12}\)

\(\dfrac{57}{76}=\dfrac{3}{4}=\dfrac{3\times3}{4\times3}=\dfrac{9}{12}\)

\(\dfrac{35}{84}=\dfrac{5}{12}\)

Gấppppppppppppppppppppppppppp

ppppppppppppppppppppppppppppp

ppppppppppppppppppppppppppppp

ppppppppppppppppppppppppppppp

\(a,\dfrac{3}{9}=\dfrac{1}{3}\\ \dfrac{16 }{24}=\dfrac{2}{3}\\ b,\dfrac{17}{51}=\dfrac{1}{3}=\dfrac{5}{15}\\ \dfrac{18}{90}=\dfrac{1}{5}=\dfrac{3}{15}\\ c,\dfrac{5}{10}=\dfrac{1}{2}=\dfrac{3}{6}\\ \dfrac{15}{45}=\dfrac{1}{3}=\dfrac{2}{6}\\ d,\dfrac{42}{63}=\dfrac{2}{3}=\dfrac{6}{9}\\ \dfrac{64}{72}=\dfrac{8}{9}\)

\(\frac{3}{5}=\frac{3\times8}{5\times8}=\frac{24}{40}\)

\(\frac{3}{8}=\frac{3\times5}{8\times5}=\frac{15}{40}\)

\(\frac{3}{10}=\frac{3\times4}{10\times4}=\frac{12}{40}\)

\(\frac{3}{2}=\frac{3\times20}{2\times20}=\frac{60}{40}\)

ghi thiếu bạn ơi

\(\frac{3}{5}=\frac{24}{40};\frac{3}{8}=\frac{15}{40};\frac{3}{10}=\frac{12}{40};\frac{3}{2}=\frac{60}{40}\)

\(\frac{3}{5}=\frac{3\times8}{5\times8}=\frac{24}{40}\)

\(\frac{3}{8}=\frac{3\times5}{8\times5}=\frac{15}{40}\)

\(\frac{3}{10}=\frac{3\times4}{10\times4}=\frac{12}{40}\)

\(\frac{3}{2}=\frac{3\times20}{2\times20}=\frac{60}{40}\)

Quy đồng mẫu số các phân số \(\frac{49}{-42};\frac{-45}{81};\frac{-24}{45}\)

Rút gọn các phân số ta được : \(\frac{49}{-42}=\frac{-49}{42}=\frac{-7}{6}\); \(\frac{-45}{81}=\frac{-5}{9}\); \(\frac{-24}{45}=\frac{-8}{15}\)

Ta có : 6 = 2 . 3

            9 = 3²

            15 = 3 . 5 

=> BCNN(6, 9, 15) = 2 . 3² . 5 = 90

90 : 6 = 15

90 : 9 = 10

90 : 15 = 6

=> \(\frac{-7}{6}=\frac{-7\cdot15}{6\cdot15}=\frac{-105}{90}\); \(\frac{-5}{9}=\frac{-5\cdot10}{9\cdot10}=\frac{-50}{90}\); \(\frac{-8}{15}=\frac{-8\cdot6}{15\cdot6}=\frac{-48}{90}\)

49/-42 = 7/-6 = -7/6
-45/81 = -5/9
-24/45 = -8/15
BCNN(6;9;15) = 90
-7/6 = -105/90
-5/9 = -50/90
-8/15 = -48/90
Vậy 49/-42 = -105/9 ; -45/81 = -50/90 ; -24/45 = -48/90
Chúc bạn học tốt!