Answer:
![\displaystyle x=\sqrt{(2U)/(k)}](https://img.qammunity.org/2021/formulas/mathematics/high-school/49dsp62elo121h6xppf38wyeopgdcwv66d.png)
The third option is the correct answer.
Explanation:
Equation Solving
We have the following equation:
![\displaystyle U=(1)/(2)kx^2](https://img.qammunity.org/2021/formulas/mathematics/high-school/r44iwu14kqrd6rtb6luukmyxgifbx3yt0f.png)
And it's required to solve it for x.
To solve this equation we need to perform some operations to have the x isolated from any other variables, constants, or operations.
This will be done by conveniently operating on both sides as follows:
Eliminate the denominator by multiplying by 2:
![\displaystyle 2U=kx^2](https://img.qammunity.org/2021/formulas/mathematics/high-school/hbfm9f6c1499wckyqtib8z8o25wl3evi8o.png)
Move k to the other side by dividing by k:
![\displaystyle (2U)/(k)=x^2](https://img.qammunity.org/2021/formulas/mathematics/high-school/1531f61pf9fj5wln1txwh1lxgaf91puq63.png)
Swapping sides to have x at the left side:
![\displaystyle x^2=(2U)/(k)](https://img.qammunity.org/2021/formulas/mathematics/high-school/7yqlurhkcvoub9btldtqasrqeody4ldoe5.png)
Taking the square root:
![\mathbf{\displaystyle x=\sqrt{(2U)/(k)}}](https://img.qammunity.org/2021/formulas/mathematics/high-school/c99boy1mat1fsgnxm0x0n0vd2vyecia7bs.png)
The third option is the correct answer.