EXPLANATION:
The first thing to do in the equation is to interchange the variables in order to do the inverse function and thus solve the equation correctly.
So the equation is as follows:
[tex]\begin{gathered} x=\sqrt[]{x^2-121} \\ Now\text{ we exchange }the\text{ variables x and y;} \\ x=\sqrt[]{y^2-121} \\ y=\sqrt[]{x^2+121};\text{ y}=-\sqrt[]{x^2+121} \\ \sqrt[]{x^2+121\text{ ; }-\sqrt[]{x^2+121}} \\ \text{the answer is : }\sqrt[]{x^2+121\text{ },\text{ }}\text{ }-\sqrt[]{x^2+121^{}} \end{gathered}[/tex]