Đáp án:
`a)(5x+1)^2=36/49`
`=>(5x+1)^2=+-(6/7)^2`
$\Rightarrow\left[\begin{matrix} 5x+1=\dfrac{6}{7}\\ 5x+1=-\dfrac{6}{7}\end{matrix}\right.⇔\left[\begin{matrix} 5x=\dfrac{6}{7}-1\\ 5x=-\dfrac{6}{7}-1\end{matrix}\right.⇔\left[\begin{matrix} 5x=-\dfrac{1}{7}\\ 5x=-\dfrac{13}{7}\end{matrix}\right.⇔\left[\begin{matrix} x=-\dfrac{1}{35}\\ x=-\dfrac{13}{35}\end{matrix}\right.$
`->x={-1/35;-13/35}`
`b)(x-2/9)^3=(2/3)^6`
`=>(x-2/9)^3=((2/3)^2)^3`
`=>x-2/9=(2/3)^2`
`=>x-2/9=4/9`
`=>x=4/9+2/9`
`=>x=6/9=2/3`
`->x={2/3}`
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