In order to make x the subject of the formula, we need to isolate the variable x on one side of the equation.
To do so, we need to calculate the square root of both sides of the equation:
[tex]\begin{gathered} x^2=10-y \\ \sqrt[]{x^2}=\sqrt[]{10-y} \\ x=\pm\sqrt[]{10-y} \end{gathered}[/tex]