Answer:
[tex]\bold{x=\sqrt{\dfrac{2U}{k}}}[/tex]
Step-by-step explanation:
[tex]U=\frac12kx^2\\\\2U=kx^2\\\\\dfrac{2U}k=x^2\\\\x=\sqrt{\dfrac{2U}k}[/tex]
or if you miswrite and it should be: U=1/(2kx^2), than
[tex]U=\dfrac1{2kx^2}\\\\\dfrac1U=2kx^2\\\\\dfrac1{2kU}=x^2\\\\x=\sqrt{\dfrac1{2kU}}[/tex]
