`Câu   13`

`a)2/3+3/5((-5)/9)`

`=2/3-3/5*5/9`

`=2/3-1/3`

`=1/3`

`b
)(-1/2)^2*4/11+7/11*(-1/2)^2`

`=(-1/2)^2(4/11+7/11)`

`=1/4*1=1/4`

`c)(-1/3)^2+7:|-1/2|-sqrt16-2022^0`

`=1/9+7:1/2-4-1`

`=1/9+7*2-5`

`=1/9+14-5`

`=1/9+9`

`=81/9`

`Câu   14`

`a)x+1/3=2/5-((-1)/3)`

`x+1/3=2/5+1/3`

`x=2/5+1/3-1/3`

`x=2/5`

`Vậy   x=2/5`

`b)6/5-|x-1/2|=3/4`

`|x-1/2|=6/5-3/4`

`|x-1/2|=2/5`

`=>x-1/2=2/5` hoặc `x-1/2=-2/5`

`x=2/5+1/2` hoặc `x=-2/5+1/2`

`x=9/10` hoặc `x=1/10`

`Vậy   x in {9/10 ; 1/10}`

`c)(3x-1/4)^2+21/25=1`

`(3x-1/4)^2=1-21/25`

`(3x-1/4)^2=4/25`

`(3x-1/4)^2=(2/5)^2`

`=>3x-1/4=2/5` hoặc `3x-1/4=-2/5`

`=>3x=2/5+1/4` hoặc `3x=-2/5+1/4`

`=>3x=13/20` hoặc `3x=-3/20`

`=>x=13/20:3` hoặc `x=-3/20 : 3`

`=>x=13/60` hoặc `x=-1/20`

`Vậy  x in {13/60; -1/20}`