Question

an object 4 cm tall is placed on the principal axis of a concave mirror of focal length 20 cm at a distance of 30 cm from its find the nature and size of the image

Answer 1

The mirror formula is
1/f=1/v+1/u
By this caluclate v
Then v/u=hi/ho
Substituye it in the 2nd formula to get size of the image
ho=8cm with -sign so we can say that the image is real and inverted.