Hi everyone,

Apologies in advance if this is the wrong place to post this.

I'm currently struggling with a question and am hoping that someone here can kindly shed some light.

A man stands in the middle of a room 17m wide and looks into a mirror on one
wall of the room. What dimensions must the mirror have in order that he can just
see the image of a rectangular patch on the opposite wall of size 7m × 4m?

I know the answer to this, but am struggling to illustrate my answer in terms of equations. Does anyone know the formulas I need to use?

Thanks in advance.