Đáp án+Giải thích các bước giải:

 `a)` `1 1/5+4/5:x=0,75`

`=>4/5:x=0,75-(1+1/5)`

`=>4/5:x=3/4-6/5`

`=>4/5:x=-9/20`

`=>x=4/5:(-9/20)`

`=>x=-16/9`

Vậy `x=-16/9`

`b)`

`1/9. 3^{4}.3^{x}=3^{7}`

`=>(1/3)^{2}.3^{4+x}=3^{7}`

`=>(3^{-1})^{2}.3^{4+x}=3^{7}`

`=>3^{4+x}=3^{7}:3^{-2}`

`=>3^{4+x}=3^{7+2}`

`=>3^{4+x}=3^{9}`

`=>4+x=9`

`=>x=5`

Vậy `x=5`

`c)`

`(x+1/2)^{2}=1/16`

`=>(x+1/2)^{2}=(1/4)^{2}=(-1/4)^{2}`

`+)TH1:x+1/2=1/4`

`=>x=1/4-1/2`

`=>x=1/4-2/4`

`=>x=-1/4`

`+)TH2:x+1/2=-1/4`

`=>x=-1/4-1/2`

`=>x=-1/4-2/4`

`=>x=-3/4`

Vậy `x\in{-1/4;-3/4}`