confused...?

Question

a real inverted image I of an object O is formed by a certain lens; the object-image seperation is D=40.0 cm, measured along the central axis of the lens. The image is just half the size of the object. (a) what kind of lens must be used to produce this image. (b) how far from the object myst the lens be placed (c) what is the focal length of the lens.

o (arrow pointing upward)____________________________axis
I (arrow pointing downward)
d is length between o and i lens is in the middle.

so if the image is real does the lens have to be convexed isn't that what it takes to get a real inverted image? please help me with all of this thank you soo much

please help anything will help

Answer 1

(a) Thin lens
(b) for a thin lens
1/S1 +1/S2=1/f
S1+S2=40 cm

Magnification M= - S2/S1= f/(f - S1)
M= -1/2
S1=2 (S2)

S1+S2=40
2 S1 + S1=40
S1=40/3
S2=(S1)/2=20/3


c) f=1/(1/S1 +1/S2)
f=S1S2/(S1+S2)