I asked
"Show mathematically that to produce an image that is the same size as the object in a concave mirror, the object needs to be at twice the focal length from the mirror."
and you answered:
"1/o + 1/o=1/f
1/2f + 1/i=1/f
1/i=1/2f
i=2f
M=di/do= 2f/2f= 1
check my thinking."
could you please explain, I'm not really following.