`#0409`

`a,`

`x/3-1/8=5/8`

`x/3=5/8+1/8`

`x/3=3/4`

`4x=9`

`x=9/4`

Vậy `x=9/4`

`b,`

`5/13 : x-1 1/26=(-5)/13`

`5/13 : x-27/26=(-5)/13`

`5/13 : x=(-5)/13+27/26`

`5/13 : x=17/26`

`x=5/13 : 17/26`

`x=10/17`

Vậy `x=10/17`

`c,`

`(x-3)/(-4)=(-9)/(x-3)`    ĐK `:x\ne3`

`(x-3)(x-3)=(-4).(-9)`

`(x-3)^2=36`

`th_1 : (x-3)^2=6^2`

`x-3=6`

`x=9` `(tm)`

`th_2 : (x-3)^2=(-6)^2`

`x-3=-6`

`x=-6+3`

`x=-3` `(tm)`

Vậy `x\in{9;-3}`

`d,`

`31/36-(1/3-x)^2=5/6`

`(1/3-x)^2=31/36-5/6`

`(1/3-x)^2=1/36`

`th_1 : (1/3-x)^2=(1/6)^2`

`1/3-x=1/6`

`x=1/3-1/6`

`x=1/6`

`th_2 : (1/3-x)^2=(-1/6)^2`

`1/3-x=-1/6`

`x=1/3-(-1/6)`

`x=1/2`

Vậy `x\in{1/6;1/2}`