Why do concave lenses always form virtual images? the rays converge the rays extend backward the rays diverge the rays intersect

The extension of the refracted rays will intersect at a point. This point is known as the focal point. Notice that a diverging lens such as this double concave lens does not really focus the incident light rays that are parallel to the principal axis; rather, it diverges these light rays.

Explanation:

the independent variable, or the one that is intentionally manipulated is the speed.