Exponential decay

The exponential function maps the real line (from minus infinity to plus infinity) to the range zero to plus infinity in a monotonically increasing manner. It is normally encountered in modelling in the form of exponential decay to a finite number. Such modelling occasionally makes mention of a half life, the amount of time taken for the quantity to halve. e.g. The decay of a radioisotope. Other examples include the cooling of a switched off kettle and the melting of an icecube.

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