a: -5/8=-225/360
7/12=210/360
8/15=192/360
b: 7/12=700/1200
-5/16=-375/1200
13/25=624/1200
c: 2/9=40/180
11/-12=-11/12=-165/180
4/-15=-4/15=-48/180
d: -4/15=-16/60
-7/20=-21/60
7/12=35/60
A/.ta có: \(8=2^3\\ 12=2^2.3\\ 15=3\cdot5\\ \Rightarrow BCNN\left(8;12;15\right)=2^3\cdot3\cdot5=120\\ \dfrac{-5}{8}=\dfrac{-5\cdot15}{8\cdot15}=\dfrac{-75}{120}; \dfrac{7}{12}=\dfrac{7\cdot10}{12\cdot10}=\dfrac{70}{120};\dfrac{8}{15}=\dfrac{8\cdot8}{15\cdot8}=\dfrac{64}{120}\)
B/ ta có: \(12=2^2\cdot3\\ 16=2^4\\ 25=5^2\\ \Rightarrow BCNN\left(12;16;25\right)=2^4\cdot3\cdot5^2=1200\\ \dfrac{7}{12}=\dfrac{7\cdot100}{12\cdot100}=\dfrac{700}{1200};\dfrac{-5}{16}=\dfrac{-5\cdot75}{16\cdot75}=\dfrac{-375}{1200};\dfrac{13}{25}=\dfrac{13\cdot48}{25\cdot48}=\dfrac{624}{1200}\)
C/ ta có : \(9=3^2\\ 12=2^2\cdot3\\ 15=3\cdot5\\ \Rightarrow BCNN\left(9;12;15\right)=2^2\cdot3^2\cdot5=180\\ \dfrac{2}{9}=\dfrac{2\cdot20}{9\cdot20}=\dfrac{40}{180};\dfrac{11}{12}=\dfrac{11\cdot15}{12\cdot15}=\dfrac{165}{180};\dfrac{1}{15}=\dfrac{1\cdot12}{15\cdot12}=\dfrac{12}{180}\)
