Bài3: Rút gọn rồi so sánh hai phân số
b) 12 phần 16 và 28 phần 21
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Cách 1 :
Rút gọn : 12/16 = 3/4 , 28/21 = 4/3
So sánh : 12/16 < 28/21
Cách 2 :
So sánh Vì 12/16 < 1 và 28/ 21 > 1 nên 28/21 > 12/16
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 \(\dfrac{8}{16}< \dfrac{5}{2}\).
\(\dfrac{5}{7}\)>\(\dfrac{6}{21}\)
\(\dfrac{18}{24}\)>\(\dfrac{15}{25}\)
\(\dfrac{12}{13}\)=\(\dfrac{1212}{1313}\)
\(\frac{16}{48}=\frac{16:16}{48:16}=\frac{1}{3}\);\(\frac{14}{35}=\frac{14:7}{35:7}=\frac{2}{5}\)
\(\frac{1}{3}=\frac{1\cdot5}{3\cdot5}=\frac{5}{15}\); \(\frac{2}{5}=\frac{2\cdot3}{5\cdot3}=\frac{6}{15}\)
ᵃ, ᵗᵃ ʳᵘ́ᵗ ᵍᵒ̣ⁿ :\(\dfrac{18}{24}=\dfrac{3}{4}\) ;
ᵗᵃ ʳᵘ́ᵗ ᵍᵒ̣ⁿ :\(\dfrac{15}{25}=\dfrac{3}{5}\)
Vì \(\dfrac{3}{4}>\dfrac{3}{5}\\ \Rightarrow\dfrac{18}{24}>\dfrac{15}{25}\)
ᵇ, ᵗᵃ ʳᵘ́ᵗ ᵍᵒ̣ⁿ :\(\dfrac{21}{15}=\dfrac{7}{5}\\ \dfrac{28}{24}=\dfrac{7}{6}\)
Vì \(\dfrac{7}{5}>\dfrac{7}{6}\\ \Rightarrow\dfrac{21}{15}>\dfrac{28}{24}\)
a, \(\dfrac{18}{24}\) = \(\dfrac{3}{4}\) \(\dfrac{15}{25}\) = \(\dfrac{3}{5}\)
\(\dfrac{3}{4}\) > \(\dfrac{3}{5}\) vậy \(\dfrac{18}{24}\) > \(\dfrac{15}{25}\)
b, \(\dfrac{21}{15}\) = \(\dfrac{7}{5}\) \(\dfrac{28}{24}\) = \(\dfrac{7}{6}\)
\(\dfrac{7}{5}\) > \(\dfrac{7}{6}\) vậy \(\dfrac{21}{15}\) > \(\dfrac{28}{24}\)
TL
12/6=2
28/21=4/3
NHÉ
HT