For the image to be at infinity, the focal length must be equal to the object distance, hence f = 60 cm.

Using the lens formula, 1/f = 1/v - 1/u, we find v = -8 cm.

Using the lens formula 1/f = 1/v - 1/u, we find v = 15 cm.

Using the lens formula 1/f = 1/v - 1/u, we find v = 20 cm.

Magnification (m) = v/u. For an object at 2f, the image distance v = 2f, so m = 2f/(2f) = 1.

Magnification (m) = image distance/object distance = 45/15 = 3.

Magnification (m) = image distance/object distance = 30/15 = 2.

Magnification (m) = -v/u = -10/20 = 0.5, but since we consider absolute value, m = 2.

Magnification (m) = -v/u = -50/25 = -2. The absolute value indicates the image is twice the size of the object.

Total power P = P1 + P2 = 5 D - 3 D = 2 D.

A concave lens always forms a virtual and upright image regardless of the object's position.

When the object is placed beyond twice the focal length, the image is real and inverted.

A convex lens forms a real and inverted image when the object is beyond the focal point.

Concave lenses always produce virtual images when the object is placed within the focal length.

A diverging lens causes parallel rays to diverge, making it impossible to focus light to a point.

A converging lens can form both real images (when the object is outside the focal length) and virtual images (when the object is within the focal length).

A diverging lens (concave) can only form virtual images.

A convex lens is used to converge light rays for hyperopic correction.