Question

[phương linh]

so sánh số hữu tỉ 

a)-15/21 và -36/44

b)-16/30 và -35/84

c)-5/91 và -501/9191

nhớ quy đồng và làm từng bước giúp tớ nhé tớ đang cần gấp

Answer 1

[Nguyễn Lê Phước Thịnh]

a: \(-\dfrac{15}{21}=\dfrac{-15:3}{21:3}=\dfrac{-5}{7}=\dfrac{-5\cdot11}{7\cdot11}=\dfrac{-55}{77}\)

\(\dfrac{-36}{44}=\dfrac{-36:4}{44:4}=\dfrac{-9}{11}=\dfrac{-9\cdot7}{11\cdot7}=\dfrac{-63}{77}\)

mà -55>-63

nên \(-\dfrac{15}{21}>-\dfrac{36}{44}\)

b: \(-\dfrac{16}{30}=\dfrac{-16:2}{30:2}=\dfrac{-8}{15}=\dfrac{-8\cdot4}{15\cdot4}=\dfrac{-32}{60}\)

\(\dfrac{-35}{84}=\dfrac{-35:7}{84:7}=\dfrac{-5}{12}=\dfrac{-5\cdot5}{12\cdot5}=\dfrac{-25}{60}\)

mà -32<-25

nên \(-\dfrac{16}{30}< -\dfrac{35}{84}\)

c: \(\dfrac{-5}{91}=\dfrac{-5\cdot101}{91\cdot101}=\dfrac{-505}{9191}\)

mà -505<-501

nên \(-\dfrac{5}{91}< -\dfrac{501}{9191}\)

Answer 2

[Dang Tung]

a) Rút gọn:

\(-\dfrac{15}{21}=-\dfrac{15:3}{21:3}=-\dfrac{5}{7}\)

\(-\dfrac{36}{44}=-\dfrac{36:4}{44:4}=-\dfrac{9}{11}\)

Quy đồng(MSC:77)

\(-\dfrac{5}{7}=-\dfrac{5.11}{7.11}=-\dfrac{55}{77}\\ -\dfrac{9}{11}=-\dfrac{9.7}{11.7}=-\dfrac{63}{77}\)

Nhận thấy: \(-\dfrac{55}{77}>-\dfrac{63}{77}\Rightarrow-\dfrac{15}{21}>-\dfrac{36}{44}\)

b) Rút gọn:

\(-\dfrac{16}{30}=-\dfrac{16:2}{30:2}=-\dfrac{8}{15}\\ -\dfrac{35}{84}=-\dfrac{35:7}{84:7}=-\dfrac{5}{12}\)

Quy đồng (MSC:60)

\(-\dfrac{8}{15}=-\dfrac{8.4}{15.4}=-\dfrac{32}{60}\\ -\dfrac{5}{12}=-\dfrac{5.5}{12.5}=-\dfrac{25}{60}\)

Nhận thấy: \(-\dfrac{32}{60}< -\dfrac{25}{60}\Rightarrow-\dfrac{16}{30}< -\dfrac{35}{84}\)

c) \(-\dfrac{5}{91}=-\dfrac{5.101}{91.101}=-\dfrac{505}{9191}< -\dfrac{501}{9191}\)