Tìm x thuộc Q biết a) 4x+1/2=-3/4 b) -1 1/3+2x=4/9 c)x/15=-7/10 d) |x+1|=3/4 -1/2 20/07/2021 Bởi Josephine Tìm x thuộc Q biết a) 4x+1/2=-3/4 b) -1 1/3+2x=4/9 c)x/15=-7/10 d) |x+1|=3/4 -1/2
Đáp án: `x = -5/16` `x = 8/9` `x = -21/2` `x ∈ { -3/4 ; -5/4 }` Lời giải: `a, 4x + 1/2 = -3/4` `⇔ 4x = -3/4 – 1/2` `⇔ 4x = -3/4 – 2/4` `⇔ 4x = -5/4` `⇔ x = -5/4 : 4` `⇔ x = -5/4 . 1/4` `⇔ x = -5/16` Vậy `x = -5/16` `b, -1 1/3 + 2x = 4/9` `⇔ -4/3 + 2x = 4/9` `⇔ 2x = 4/9 + 4/3` `⇔ 2x = 4/9 + 12/9` `⇔ 2x = 16/9` `⇔ x = 16/9 : 2` `⇔ x = 16/9 . 1/2` `⇔ x = 8/9` Vậy `x = 8/9` `c, x/15 = -7/10` `⇔ 10x = 15 . (-7)` `⇔ 10x = -105` `⇔ x = (-105) : 10` `⇔ x = -21/2` Vậy `x = -21/2` `d, |x + 1| = 3/4 – 1/2` `⇔ |x + 1| = 3/4 – 2/4` `⇔ |x + 1| = 1/4` `⇔` \(\left[ \begin{array}{l}x+1=\frac{1}{4}\\x+1=\frac{-1}{4}\end{array} \right.\) `⇔` \(\left[ \begin{array}{l}x=\frac{1}{4} – 1 = \frac{1}{4} – \frac{4}{4} = \frac{-3}{4}\\x=\frac{-1}{4} – 1 = \frac{-1}{4} – \frac{4}{4} = \frac{-5}{4}\end{array} \right.\) Vậy `x ∈ { -3/4 ; -5/4 }` Bình luận
Đáp án:
`x = -5/16`
`x = 8/9`
`x = -21/2`
`x ∈ { -3/4 ; -5/4 }`
Lời giải:
`a, 4x + 1/2 = -3/4`
`⇔ 4x = -3/4 – 1/2`
`⇔ 4x = -3/4 – 2/4`
`⇔ 4x = -5/4`
`⇔ x = -5/4 : 4`
`⇔ x = -5/4 . 1/4`
`⇔ x = -5/16`
Vậy `x = -5/16`
`b, -1 1/3 + 2x = 4/9`
`⇔ -4/3 + 2x = 4/9`
`⇔ 2x = 4/9 + 4/3`
`⇔ 2x = 4/9 + 12/9`
`⇔ 2x = 16/9`
`⇔ x = 16/9 : 2`
`⇔ x = 16/9 . 1/2`
`⇔ x = 8/9`
Vậy `x = 8/9`
`c, x/15 = -7/10`
`⇔ 10x = 15 . (-7)`
`⇔ 10x = -105`
`⇔ x = (-105) : 10`
`⇔ x = -21/2`
Vậy `x = -21/2`
`d, |x + 1| = 3/4 – 1/2`
`⇔ |x + 1| = 3/4 – 2/4`
`⇔ |x + 1| = 1/4`
`⇔` \(\left[ \begin{array}{l}x+1=\frac{1}{4}\\x+1=\frac{-1}{4}\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=\frac{1}{4} – 1 = \frac{1}{4} – \frac{4}{4} = \frac{-3}{4}\\x=\frac{-1}{4} – 1 = \frac{-1}{4} – \frac{4}{4} = \frac{-5}{4}\end{array} \right.\)
Vậy `x ∈ { -3/4 ; -5/4 }`