In an experiment to determine the focal length $\mathrm{f}$ of a concave mirror by the $\text{u}-\mathrm{\upsilon }$method, a student places the object pin $\mathrm{A}$ on the principal axis at a distance $\mathrm{x}$ from the pole $\mathrm{P}$. The student looks at the pin and its inverted image from a distance keeping his/her eye in line with $\mathrm{PA}$. When the student shifts his/her eye towards left, the image appears to the right of the object pin. Then