Bài `2:`

`b) B = (-4)/(13) + 3/5 + 1/3 - 9/13 + 2/5`

`=> B = (-4)/(13) + 3/5 + 1/3 + (-9)/(13) + 2/5`

`=> B = [(-4)/(13) + (-9)/(13)] + (3/5 + 2/5) + 1/3`

`=> B = (-1) + 1 + 1/3`

`=> B = 0 + 1/3`

`=> B = 1/3`

`c) C = 6/21 - (-12)/(44) + 10/14 - (1)/(-4) - 18/33`

`=> C = 6/21 + 12/44 + 10/14 + 1/4 + (-18)/(33)`

`=> C = 2/7 + 3/11 + 5/7 + 1/4 + (-6)/(11)`

`=> C = (2/7 + 5/7) + [3/11 + (-6/11)] + 1/4`

`=> C = 1 + (-3/11) + 1/4`

`=> C = 8/11 + 1/4`

`=> C = 43/44`

SAI THÌ BẢO MIK NHA^^

Đáp án+Giải thích các bước giải:

$\\$ `b,B=(-4)/13+3/5+1/3-9/(13)+2/5`

$\\$ `=((-4)/13-9/(13))+(3/5+2/5)+1/3`

$\\$ `=(-13)/(13)+5/5+1/3`

$\\$ `=-1+1+1/3=1/3`

$\\$ Vậy `B=1/3`

$\\$ `c,C=6/(21)-(-12)/(44)+(10)/(14)-1/(-4)-(18)/33`

$\\$ `=(2.3)/(7.3)-(-3.4)/(11.4)+(5.2)/(7.2)+1/4-(6.3)/(11.3)`

$\\$ `=2/7+3/(11)+5/7+1/4-6/(11)`

$\\$ `=(2/7+5/7)+(3/11-6/11)+1/4`

$\\$ `=7/7-(3)/(11)+1/4`

$\\$ `=1-3/(11)+1/4`

$\\$ `=(11)/(11)-3/(11)+1/4`

$\\$ `=8/(11)+1/4`

$\\$ `=(32)/(44)+(11)/(44)`

$\\$ `=(43)/(44)`

$\\$ Vậy `C=(43)/(44)`