`a)`
Để `x^3+3x` có nghiệm
`\to x^3+3x=0`
`\to x(x^2+3)=0`
`\to` \(\left[ \begin{array}{l}x=0\\x^2+3=0\end{array} \right.\) `\to` \(\left[ \begin{array}{l}x=0\\x^2=-3(L)\end{array} \right.\)
Vậy `x=0`
`b)`
Để `2x^2-x` có nghiệm
`\to2x^2-x=0`
`\to x(2x-1)=0`
`\to` \(\left[ \begin{array}{l}x=0\\2x-1=0\end{array} \right.\) `\to` \(\left[ \begin{array}{l}x=0\\x=\dfrac{1}{2}\end{array} \right.\)
Vậy `x\in{0;1/2}`
`c)`
Để `4x-2/3` có nghiệm
`\to 4x-2/3=0`
`\to 4x=2/3`
`\to x=2/3:4`
`\to x=2/3 . 1/4`
`\to x=2/12`
`\to x=1/6`
Vậy `x=1/6`
