To solve this problem, consider the following picture
By the tangent secant segment theorem we have the following equation

Note that in our case, we have a=x, b=3 and c=9. So if we replace this values in the equation, we have

so, applying the square root on both sides, we get
![x=\sqrt[]{36}=\pm6](https://img.qammunity.org/2023/formulas/mathematics/college/how2rrfoy1xbu9w798ag0k5ujm21jn3zma.png)
Since x is a distance, it should be strictly positive, so we have that
