Concave function Concave function In mathematics, a concave function is the negative of a convex function. A concave function is also synonymously called concave downwards, concave down, convex upwards, convex cap or upper convex. A real-valued function formula_1 on an interval (or, more generally, a convex set in vector space) is said to be "concave" if, for any formula_2 and formula_3 in the interval and for any formula_4, A function is called "strictly concave" if for any formula_7 and formula_8. For a function formula_9, this second definition merely states that for every formula_10 strictly between formula_2 and formula_3, the point formula_13 on
Lens (optics) real object at the location of that virtual image. Likewise, it appears to a subsequent lens as if it were an object at that location, so that second lens could again focus that light into a real image, "S" then being measured from the virtual image location behind the first lens to the second lens. This is exactly what the eye does when looking through a magnifying glass. The magnifying glass creates a (magnified) virtual image behind the magnifying glass, but those rays are then re-imaged by the lens of the eye to create a "real image" on the retina.