Dễ lắm
a) 1 . -13 hay -1 .13
b) -15 .1 
    -3 .5
     -5 .3 
     -1 .15
c) -27 .1; -1 .27; -9 . 3; -3. 9

a) - 13 =  -1. 13 

           = -13.1  

b) - 15  = -3.5

            = -5.3

            = -1.15

            = -15.1     

c) - 27 = -1.27

           = -27.1

           = -3.9

           = -9.3

a) 1.-13 hay-1.13

b)-15.1

-3.5

-5.3

-1.15

c)-27.1

-3.9

-9.3

-1.27

Ta viết được như sau:  − 27 = 9. − 3 = 3. − 9

Bài 2:

\(\frac{13}{36}=\frac{1+5+7}{36}=\frac{1}{36}+\frac{5}{36}+\frac{7}{36}\)

\(\frac{31}{60}=\frac{1+23+7}{60}=\frac{1}{60}+\frac{23}{60}+\frac{7}{60}\)

Bài 1:

\(\frac{25}{27}=\frac{1+3+9+3+9}{27}=\frac{1}{27}+\frac19+\frac13+\frac19+\frac13\)

\(\frac{15}{16}=\frac{8+7}{16}=\frac12+\frac{7}{16}=\frac12+\frac{4+3}{16}=\frac12+\frac14+\frac{3}{16}\)

\(=\frac12+\frac14+\frac{2+1}{16}=\frac12+\frac14+\frac18+\frac{1}{16}\)

a: \(\frac{13}{27}=\frac{1}{27}+\frac{12}{27}=\frac{1}{27}+\frac49=\frac{1}{27}+\frac{3+1}{9}=\frac{1}{27}+\frac39+\frac19\)

\(=\frac{1}{27}+\frac19+\frac13\)

b: \(\frac{15}{16}=\frac{1}{16}+\frac{14}{16}\)

\(=\frac{1}{16}+\frac78=\frac{1}{16}+\frac{4+3}{8}=\frac{1}{16}+\frac48+\frac38\)

\(=\frac{1}{16}+\frac12+\frac{2+1}{8}=\frac{1}{16}+\frac12+\frac14+\frac18\)

c: \(\frac{39}{54}=\frac{38+1}{54}=\frac{38}{54}+\frac{1}{54}\)

\(=\frac{1}{54}+\frac{19}{27}=\frac{1}{54}+\frac{1}{27}+\frac{18}{27}\)

\(=\frac{1}{54}+\frac{1}{27}+\frac23=\frac{1}{54}+\frac{1}{27}+\frac46=\frac{1}{54}+\frac{1}{27}+\frac36+\frac16\)

\(=\frac{1}{54}+\frac{1}{27}+\frac16+\frac12\)

d: \(\frac{13}{42}=\frac{6+7}{42}=\frac{6}{42}+\frac{7}{42}=\frac17+\frac16\)

Ta viết được như sau:  − 13 = 13. − 1 = − 13 .1

a)-13x1

b)-5x3,-3x5

c)-9x3,-3x9

d)17x2

e)6x2

a)-13= -1 *13 

b) -15 = -5*3

c) -27 = -3*9

d) 34=2*17

e) 12 = 6*2

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