Đáp án:
`1)` `x=7/15` `5)` `x=2 hoặc x=31/20`
`2)` `x=-13/72` `6)` `x=-28/35`
`3)` `x=-46/35` `7)` `x=-2/3`
`4)` `x=2/3` `8)` `x=-43/28 hoặc x=71/28`
Giải thích các bước giải:
Bài 2:
`1)` `1/5+x=2/3`
`⇒ x=2/3-1/5`
`⇒ x=(10-3)/(3*5)`
`⇒ x=7/15`
Vậy `x=7/15`
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`2)` `-5/8+x=4/9`
`⇒ x=4/9-5/8`
`⇒ x=(32-45)/(9*8)`
`⇒ x=-13/72`
Vậy `x=-13/72`
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`3)` `1 3/4x+1 1/2=-4/5`
`⇒ 1 3/4x =-4/5-1 1/2`
`⇒ 7/4x =-4/5-3/2`
`⇒ x =-(8+15)/(5*2):7/4`
`⇒ x =-23/10*4/7`
`⇒ x =-(23*2)/(5*7)`
`⇒ x =-46/35`
Vậy `x=-46/35`
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`4)` `1/4+3/4x=3/4`
`⇒ 3/4x=3/4-1/4`
`⇒ 3/4x=2/4`
`⇒ x=1/2:3/4`
`⇒ x=1/2*4/3`
`⇒ x=2/3`
Vậy `x=2/3`
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`5)` `(-3)/4-|4/5-x|=-1`
`⇒ |4/5-x|=(-3)/4-(-1)`
`⇒ |4/5-x|=1-3/4`
`⇒ |4/5-x|=1/4`
`⇒`$\left \{ {{\dfrac{4}{5}-x=\dfrac{1}{4}} \atop {\dfrac{4}{5}-x=-\dfrac{1}{4}}} \right.$ `⇒`$\left \{ {{x=\dfrac{4}{5}-\dfrac{1}{4}} \atop {x=\dfrac{4}{5}+\dfrac{1}{4}}} \right.$ `⇒`$\left \{ {{\dfrac{16-6}{5.4}} \atop {\dfrac{16+15}{5.4}}} \right.$ `⇒`$\left \{ {{x=\dfrac{10}{5.4}} \atop {x=\dfrac{31}{5.4}}} \right.$ `⇒`$\left \{ {{x=2} \atop {x=\dfrac{31}{20}}} \right.$
Vậy `x=2` hoặc `x=31/20`
`6)` `3/35-(3/5+x)=2/7`
`⇒ 3/5+x =3/35-2/7`
`⇒ x =3/35-2/7-3/5`
`⇒ x =(3-10-21)/35`
`⇒ x =(-28)/35`
Vậy `x=-28/35`
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`7)` `3/7+1/7:x=3/14`
`⇒ 1/7:x=3/14-3/7`
`⇒ x=1/7:(3-6)/(14)`
`⇒ x=1/7*14/-3`
`⇒ x=-2/3`
Vậy `x=-2/3`
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`8)` `-5/7-|1/2-x|=-11/4`
`⇒ |1/2-x|=-5/7-(-11/4)`
`⇒ |1/2-x|=-5/7+11/4`
`⇒ |1/2-x|=(-20+77)/(7*4)`
`⇒ |1/2-x|=57/28`
`⇒`$\left \{ {{\dfrac{1}{2}-x=\dfrac{57}{28}} \atop {\dfrac{1}{2}-x=-\dfrac{57}{28}}} \right.$ `⇒`$\left \{ {{x=\dfrac{1}{2}-\dfrac{57}{28}} \atop {x=\dfrac{1}{2}+\dfrac{57}{28}}} \right.$ `⇒`$\left \{ {{x=\dfrac{14-57}{28}} \atop {x=\dfrac{14+57}{28}}} \right.$ `⇒`$\left \{ {{x=\dfrac{-43}{28}} \atop {x=\dfrac{71}{28}}} \right.$
Vậy `x=-43/28` hoặc `x=71/28`
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