Use the mirror equation to deduce that :
a) an object placed between f and 2f of a concave mirror produces a real image beyond 2f.
[Note : The exercise helps you deduce algebraically properties of images that one obtains from explicit ray diagrams.]

Explanation

Apply mirror equation and the condition:
(a) `flt0` (concave mirror), `u lt 0` (object on left)
(b) `f gt 0, u lt 0`
(c) `f gt 0 " (convex mirror) and "v lt0`
(d) `f lt 0" (concave mirror), "f lt u lt 0`
to deduce the desuired result.