`a,`
`(5x + 1)^{2} = 36/49`
$\Leftrightarrow$ `(5x + 1)^{2} = (+- 6/7)^{2}`
$\text{TH1:}$
`5x + 1 = 6/7`
$\Leftrightarrow$ `5x = 6/7 - 1`
$\Leftrightarrow$ `5x = -1/7`
$\Leftrightarrow$ `x = -1/7 : 5`
$\Leftrightarrow$ `x = -1/35`
$\text{TH2:}$
`5x + 1 = -6/7`
$\Leftrightarrow$ `5x = -6/7 - 1`
$\Leftrightarrow$ `5x = -13/7`
$\Leftrightarrow$ `x = -13/7 : 5`
$\Leftrightarrow$ `x = -13/35`
$\text{Vậy}$ `x \in {-1/35 ; {-13}/35}`
______________________
`b,`
`(x - 2/9)^{3} = (2/3)^{6}`
$\Leftrightarrow$ `x - 2/9 = (2/3)^{2}`
$\Leftrightarrow$ `x- 2/9 = 4/9`
$\Leftrightarrow$ `x = 4/9 + 2/9`
$\Leftrightarrow$ `x = 2/3`
$\text{Vậy}$ `x = 2/3`
