Question

tính : 

a) 4/5 + 4/-18

b) 7/21 + 9/-36

c) 1/-8 + -5/9

d) 4/13 + -(-12)/39

e) -(-1)/21 + 1/28

g) 18/24 + 35/-10

Answer 1

`#` `\text{dkhanhqlv}`

`a)4/5+4/(-18)`

`=4/5+(-4/18)`

`=72/90+(-20/90)`

`=52/90`

`=26/45`

`b)7/21+9/(-36)`

`=1/3+(-9/36)`

`=1/3+(-1/4)`

`=4/12+(-3/12)`

`=1/12`

`c)1/(-8)+(-5/9)`

`=-1/8-5/9`

`=-9/72-45/72`

`=-49/72`

`d)` Đề phần này là sao nhỉ ?

`e)-(-1)/21 + 1/28`

`= 1/21 + 1/28`

`= 4/84+3/84`

`=7/84`

`g)18/24+35/(-10)`

`=18/24+(-35/10)`

`=90/120+(-420/120)`

`=-330/120`

`=-11/4`

Answer 2

\(a,\dfrac{4}{5}+\dfrac{4}{-18}=\dfrac{72}{90}+\dfrac{-120}{90}=\dfrac{-48}{90}=\dfrac{-8}{15}\)

\(b,\dfrac{7}{21}+\dfrac{9}{-36}=\dfrac{1}{3}+\dfrac{-1}{4}=\dfrac{4}{12}+\dfrac{-3}{12}=\dfrac{1}{12}\)

\(c,\dfrac{1}{-8}+\dfrac{-5}{9}=\dfrac{-9}{72}+\dfrac{-40}{72}=\dfrac{-49}{72}\)

\(d,\dfrac{4}{13}+\left(-\dfrac{-12}{39}\right)=\dfrac{4}{13}+\dfrac{12}{39}=\dfrac{4}{13}+\dfrac{4}{13}=\dfrac{8}{13}\)

\(e,\left(-\dfrac{-1}{21}\right)+\dfrac{1}{28}=\dfrac{4}{84}+\dfrac{3}{84}=\dfrac{7}{84}=\dfrac{1}{12}\)

\(g,\dfrac{18}{24}+\dfrac{35}{-10}=\dfrac{3}{4}+\dfrac{-7}{2}=\dfrac{3}{4}+\dfrac{-14}{4}=\dfrac{-11}{4}\)