Đáp án:
`a. (x-2/5)^2=16`
`<=> x-2/5=+-4`
`<=>`\(\left[ \begin{array}{l}x-\dfrac{2}{5}=4\\x-\dfrac{2}{5}=-4\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=\dfrac{22}{5}\\x=-\dfrac{18}{5}\end{array} \right.\)
Vậy `x\in{-18/5;22/5}`
`b. 3.(3x-1/2)^3+1/9=0`
`<=> 3.(3x-1/2)^3=-1/9`
`<=> (3x-1/2)^3=(-1/9):3`
`<=> (3x-1/2)^3=(\frac{-1}{9}).\frac{1}{3}`
`<=> (3x-1/2)^3=\frac{-1}{27}`
`<=> (2x-1/2)^3=(\frac{-1}{3})^3`
`<=> 3x-1/2=\frac{-1}{3}`
`<=> 3x=\frac{-1}{3}+\frac{1}{2}`
`<=> 3x=\frac{-2+3}{6}`
`<=> 3x=\frac{1}{6}`
`<=> x=\frac{1}{6}:3`
`<=> x=\frac{1}{6}xx\frac{1}{3}`
`<=> x=\frac{1}{6xx3}`
`<=> x=\frac{1}{18}`
Vậy `x\in{1/18}`
