Magnification of a convex lens is

For which position of the object, magnification of convex lens is -1.(minus one) ?

For which position of the object magnification of convex lens is -1 (minus one) ?

(a) The linear magnification of a concave lens is always positive. Why? (b) The linear magnification of a convex lens may be positive or negative. Why ?

The magnification power of a convex lens of focal length 10cm, when the image is formed at the near point is

The magnification power of a convex lens of focal length 10cm, when the image is formed at the near point is