The given triangle is a right angle triangle as the radius is perpendicular to the tangent to the circle.
The unknown side is opposite to the right angle hence it will be the hypotenuse of the triangle.
The unknown side can be determined as,
![\begin{gathered} x=\sqrt[]{12^2+16^2} \\ =\sqrt[]{144+256} \\ =\sqrt[]{400} \\ =20 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/qmo4e27ftdyzvd1paieo4s5irib4uc3l76.png)
Thus, the value of the missing side is 20.