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  2. Real image - Wikipedia

    en.wikipedia.org/wiki/Real_image

    A real image occurs at points where rays actually converge, whereas a virtual image occurs at points that rays appear to be diverging from. Real images can be produced by concave mirrors and converging lenses, only if the object is placed further away from the mirror/lens than the focal point, and this real image is inverted. As the object ...

  3. Concave polygon - Wikipedia

    en.wikipedia.org/wiki/Concave_polygon

    An example of a concave polygon. A simple polygon that is not convex is called concave, [1] non-convex [2] or reentrant. [3] A concave polygon will always have at least one reflex interior angle—that is, an angle with a measure that is between 180 degrees and 360 degrees exclusive. [4]

  4. Hollow Earth - Wikipedia

    en.wikipedia.org/wiki/Hollow_Earth

    An example of a concave hollow Earth. Humans live on the interior, with the universe in the center. Instead of saying that humans live on the exterior surface of a hollow planet, sometimes called a "convex" Hollow Earth hypothesis, it is hypothesized humans live on the interior surface. This has been called the "concave" Hollow Earth hypothesis ...

  5. Concave function - Wikipedia

    en.wikipedia.org/wiki/Concave_function

    The sum of two concave functions is itself concave and so is the pointwise minimum of two concave functions, i.e. the set of concave functions on a given domain form a semifield. Near a strict local maximum in the interior of the domain of a function, the function must be concave; as a partial converse, if the derivative of a strictly concave ...

  6. Curved mirror - Wikipedia

    en.wikipedia.org/wiki/Curved_mirror

    A concave mirror, or converging mirror, has a reflecting surface that is recessed inward (away from the incident light). Concave mirrors reflect light inward to one focal point. They are used to focus light. Unlike convex mirrors, concave mirrors show different image types depending on the distance between the object and the mirror.

  7. Metric space - Wikipedia

    en.wikipedia.org/wiki/Metric_space

    For example, [0, 1] is the completion of (0, 1), and the real numbers are the completion of the rationals. Since complete spaces are generally easier to work with, completions are important throughout mathematics. For example, in abstract algebra, the p-adic numbers are defined as

  8. Martingale (probability theory) - Wikipedia

    en.wikipedia.org/wiki/Martingale_(probability...

    Similarly, a concave function of a martingale is a supermartingale. Martingales and stopping times ... An example in real life might be the time at which a gambler ...

  9. Virtual image - Wikipedia

    en.wikipedia.org/wiki/Virtual_image

    In contrast, a real image can be projected on the screen as it is formed by rays that converge on a real location. A real image can be projected onto a diffusely reflecting screen so people can see the image (the image on the screen plays as an object to be imaged by human eyes). [2] A plane mirror forms a virtual image positioned behind the ...