Assuming the principal axis as the $x$-axis and the optical centre as the origin, how will you determine the signs of the quantities $u, v$ and $f$ for a lens?

An extended object is placed perpendicular to the principal axis of a convex lens. Draw neat diagrams to show the image formation in the following cases,

(a) The object is at a distance that is more than double the focal length of the lens,

(b) The object is at a distance equal to double the focal length,

(c) The object is at a distance that is more than its focal length but is less than double the focal length.