A concave mirror can form a real image where checked reflected rays meet in front of the mirror.
Example
A concave mirror can form a real image where checked reflected rays meet in front of the mirror. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
A concave mirror has a front focus
Use a concave mirror with focal length 6 metres. Put the object 12 metres in front of the mirror, outside the focus.
f=6mu=12m
Reflected rays agree on the image
The vertex ray and the parallel-to-focus ray meet at the same front-side point. That agreement is the real mirror image.
reflected ray intersection=image point
Object distance changes the meeting point
Hold the concave focal length fixed. Moving the object changes where the reflected rays meet and changes the inverted scale.
f6m6m6mu18m12m9mv9m12m18mm2−1−1−2
opticsThe image point is accepted only when independent reflected-ray geometry agrees with the mirror equation.