We have the equation of y as a function of x:
[tex]y(x)=x^2+m[/tex]To find x(y) we just need to solve for x, first by subtracting m from both sides
[tex]y-m=x^2[/tex]Now, we just have to take the square root on both sides
Taking the square root of a number it's actually raising it to the 1/2 power:
[tex]\sqrt[]{a}=a^{\frac{1}{2}}[/tex]Now, when we proceed to raise the square root of a number to two, we can arrange it like this:
[tex](a^{\frac{1}{2}})^2=a^{\frac{2}{2}}=a^1=a[/tex]When we take the square root of a number that is raised to two the result will be the number without any power, like this:
[tex]\sqrt[]{a^2}=a[/tex]Then:
[tex]\sqrt[]{x^2}=x=\sqrt[]{y-m}[/tex]