Câu $6$.
$c$) `A = (5 - 1/7 + 2/5) - (3 + 2/7 - 4/5) - (4 + 4/7 - 1/5)`
`A = 5 - 1/7 + 2/5 - 3 - 2/7 + 4/5 - 4 - 4/7 + 1/5`
`A = (5 - 3 - 4) - (1/7 + 2/7 + 4/7) + (2/5 + 4/5 + 1/5)`
`A = -2 - 1 + 7/5`
`A = -3 + 7/5`
`A = -8/5`
$d$) `(2/7 - 3/16) : 4/9 - (9/7 + 13/16) : 4/9`
`= (2/7 - 3/16) . 9/4 - (9/7 + 13/16) . 9/4`
`= 9/4 . (2/7 - 3/16 - 9/7 - 13/16)`
`= 9/4 . (-7/7 - 16/16)`
`= 9/4 . (-2)`
`= -9/2`
$e$) `2/7 : (1/4 - 3/5) + 2/7 : (3/4 - 1/5)`
`= 2/7 . {-20}/7 + 2/7 . 20/11`
`= 2/7 . {-80}/77`
`- -160/539`
Câu $7$.
$a$) `(2x-4)(x - 1/2) = 0`
`⇒` \(\left[ \begin{array}{l}x=2\\x=\dfrac{1}{2}\end{array} \right.\)
Vậy $x$ $∈$ `{2;1/2}`
$b$) `{2x}/5 = 24/15`
`⇔ 2x.15 = 5.24`
`⇔ 30x = 120`
`⇔ x = 4`
Vậy $x=4$
$c$) `1/2 x - 0,25 = 2/3 x + 3/4`
`⇔ 1/2 x - 2/3 x = 3/4 + 1/4`
`⇔ x . (1/2 - 2/3) = 1`
`⇔ x . -1/6 = 1`
`⇔ x = -6`
Vậy `x=-6`
