Đáp án:
`a,A=27/23+5/21-4/23+16/21+1/2`
`A=(27/23-4/23)+(5/21+16/21)+1/2`
`A=23/23+21/21+1/2`
`A=1+1+1/2`
`A=2+1/2`
`A=5/2`
`b)B=6.(-1/3)^3 - 3.(-1/3)^2-2.(-1/3)+1`
`=3(-1/3)^2[2(-1/3)-1]-[2(-1/3)-1]`
`=[2(-1/3)-1][3(-1/3)^2-1]`
`=(-2/3-1)(3 . 1/9-1)`
`=(-5/3).(1/3-1)`
`=(-5/3).(-2/3)`
`=10/9`