Rút gọn các phân số sau về phân số tối giản:
12/30 ................\(=\dfrac{12:6}{30:6}=\dfrac{2}{5}\)...........................................

20/45 ....................\(=\dfrac{20:5}{45:5}=\dfrac{4}{9}\)......................................

28/70.....................\(=\dfrac{28:14}{70:14}=\dfrac{2}{5}\).......................................

Rút gọn các phân số sau về phân số tối giản:
12/30 ..= 6/15........................................................

20/45 ..=4/9........................................................

28/70..=14/5..........................................................

34/51..=2/3..........................................................

215/300..=43/20.....................................................

1200/2010..=120/201.................................................

\(\dfrac{35}{45}=\dfrac{35:5}{45:5}=\dfrac{7}{9}\)

7/9

7/9 

\(\dfrac{20}{45}=\dfrac{20:5}{45:5}=\dfrac{4}{9}\)

=4/9

4/9

`= 1/3`

`= 1/2`

`= 5/9`

`= 23/49`.

1/3
1/2
5/9
23/49

\(\dfrac{45}{135}=\dfrac{1}{3};\dfrac{117}{234}=\dfrac{3}{2};\dfrac{1515}{2727}=\dfrac{5}{9};\dfrac{232323}{494949}=\dfrac{23}{49}\)

a )   − 18 − 27 = ( − 18 ) : ( − 9 ) ( − 27 ) : ( − 9 ) = 2 3

b )   45 − 24 = 45 : ( − 3 ) ( − 24 ) : ( − 3 ) = − 15 8

\(\dfrac{90}{120}=\dfrac{30.3}{30.4}=\dfrac{3}{4}\)

\(\dfrac{15}{25}=\dfrac{5.3}{5.5}=\dfrac{3}{5}\)

\(\dfrac{18}{45}=\dfrac{9.2}{9.5}=\dfrac{2}{5}\)

\(\dfrac{36}{64}=\dfrac{4.9}{4.16}=\dfrac{9}{16}\)

\(\dfrac{32}{72}=\dfrac{8.4}{8.9}=\dfrac{4}{9}\)

\(\dfrac{84}{49}=\dfrac{7.12}{7.7}=\dfrac{12}{7}\)

\(\dfrac{90}{120}=\dfrac{3}{4};\dfrac{15}{25}=\dfrac{3}{5};\dfrac{18}{45}=\dfrac{2}{5};\dfrac{36}{64}=\dfrac{9}{16};\dfrac{32}{72}=\dfrac{4}{9};\dfrac{84}{49}=\dfrac{12}{7}\)

\(\dfrac{3}{4},\dfrac{3}{5},\dfrac{2}{5},\dfrac{9}{16},\dfrac{4}{9},\dfrac{12}{7}\)

12/30=6/15

20/45=4/9

28/70=2/5

34/51=2/3

Rút gọn các phân số sau 12/30

20/45.   28/70.    34/51

BL:

12/30=6/15

20/45=4/9

28/70=2/5

34/51=2/3

TL:

12/30=6/15

20/45=4/9

28/70=2/5

34/51=2/3

k mik nha bn

Hướng dẫn: Chia cả tử và mẫu cho UCLN của chúng:

ƯCLN(20, -140 ) = 20. Do đó: