If the corresponding function value f(x) is unique for each independent variable x in the definition domain, it is said that f(x) is a single-valued function.

The functions involved in middle school mathematics are all single-valued functions. Mathematics, a public course for non-mathematics majors in universities, generally refers to this single-valued function.

Exponential function is an important function in mathematics. This function applied to the value e is written as exp(x). It can also be written as ex, where e is a mathematical constant and the base of natural logarithm, which is about equal to 2.7 1828 1828, also known as Euler number.

Extended information of exponential function

As a function of the real variable x, the image of y=ex is always positive (above the x axis) and increasing (from left to right). It never touches the X axis, although it can be infinitely close to the X axis (therefore, the X axis is the horizontal asymptote of this image. Its inverse function is natural logarithm ln(x), which is defined on all positive numbers X.

The important point of exponential function based on E is that its function is equal to its derivative. E is irrational number and transcendental number (see Lin Deman-Webster theorem. This is the first certified transcendental number, not deliberately constructed; Proved by Charles Hermite in 1873.