An object placed at a distance of a 9cm from the first principal focus of a convex lens produces a real image at a distance of 25cm. from its second principal focus. then the focal length of the lens is :

An object is kept at a distance of 4 cm form the first focus of a convex lens. A real image is formed at a distance of 9 cm from its second focus. What is the focal length of that lens is ___________(in cm)

With a concave mirror, an object is placed at a distance 9cm from the principal focus, on the principal axis. The image is formed at a distance 16cm from the principal focus. The focal length of the mirror is

An object is placed at a distance x_1 from the principal focus of a lens and its real image is formed at a distance x_2 from the another principal focus. The focal length of the lens is

With a concave mirrorr, an object is placed at a distance x_(1) from the principal focus, on the principal axis. The image is formed at a distance x_(2) from the principal focus. The focal length of the mirrorr is

With a concave mirror, an object is placed at a distance x_(1) from the principal focus, on the principal axis. The image is formed at a distance x_(2) from the principal focus. The focal length of the mirror is

An object is put at a distance of 5cm from the first focus of a convex lens of focal length 10cm. If a real image is formed, its distance from the lens will be