Basic geometry skills?

The mirror, the object, and the camera form a triangle.  You know their locations (x/z coordinates) to be able to determine the lengths of each side.  Link to equation.

From that you can get an angle.  Then you can use said angle (solve for mirror's location) to figure out which angle the mirror needs to be pointed in order to see the reflection from the camera.

WARK!

Thus Spoketh Winterclaw: a blog about a Winterclaw who speaks from time to time.

 

(using Poser Pro 2014 SR3, on 64 bit Win 7, poser units are inches.)