Bài 13:
a, `\frac{7}{-15}; \frac{-8}{-25} ; \frac{11}{-75}`
MSC: `-75`
`\frac{7}{-15} = \frac{7.5}{(-15).5}= \frac{35}{-75}`
`\frac{-8}{-25}= \frac{(-8).3}{(-25).3} =\frac{-24}{-75} `
`\frac{11}{-75} = frac{11}{-75}`
b, `\frac{-8}{-45}; \frac{13}{-180}; \frac{-4}{-30}`
MSC: `-180`
`\frac{-8}{-45} = \frac{(-8).4}{(-45).4} \frac{-32}{-180}`
`\frac{13}{-180} = \frac{13}{-180}`
`\frac{-4}{-30} = \frac{(-4).6}{(-30).6} = \frac{-24}{-180}`
Bài 14:
`\frac{-1}{8} = \frac{(-1).3}{8.3} = \frac{-3}{24}`
`\frac{2}{-3} = \frac{2.(-8)}{(-3).(-8)} = \frac{-16}{24}`
`\frac{-1}{-2} = \frac{(-1).(-12)}{(-2).(-12)} =\frac{12}{24}`
`\frac{3}{-72} = \frac{3:(-3)}{(-72):(-3)} = \frac{-1}{24}`
`\frac{5}{-6} = \frac{5.(-4)}{(-6).(-4)} = \frac{-20}{24}`
Bài 15:
`1=1/1 = \frac{1.16}{1.16} = \frac{16}{16}`
` -7 = -7/1 = \frac{(-7).16}{1.16} = \frac{-112}{16}`
`\frac{5}{-8} = \frac{5.(-2)}{(-8).(-2)} = \frac{-10}{16}`
Bài 16:
`\frac{5.6+5.7}{5.8+20} = \frac{65}{60} = \frac{13}{12}`
`\frac{8.9-4.15}{12.7-180} = \frac{72-60}{84-180} = \frac{-12}{96} = \frac{-1}{8}`
`=>MSC: 24`
`=> \frac{13}{12} = \frac{13.2}{12.2} = \frac{26}{24}`
`=> \frac{-1}{8} = \frac{(-1).3}{8.3} = \frac{-3}{24}`
