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Function definition, need to pay attention to.

The (1) function is the correspondence of two groups of non-empty numbers, and the domain cannot be an empty set, otherwise it is not a function.

(2) The domain of the function is set a; Range is a subset of set b, which can be equal or unequal.

(3) According to the definition of function, there is only one corresponding function value for any number in the definition domain. From the function image, it is impossible for any two points on the image to be symmetrical about X axis.

Conceptual knowledge of functions

The concept of modern function is described by sets: given two non-empty real number sets A and B and the corresponding relation F, if there is a unique definite real number Y corresponding to X in set B for each real number X in set A. ..

Then f(x) is called a function defined on set A, and it is denoted as y=f(x). X is called independent variable, Y is called dependent variable, the range of independent variable (number set A) is called the domain of function, and the set of all function values is called the domain of function.

Besides, in daily life, we should pay attention to the fact that function is the basis and focus of high school mathematics. Accurately understanding and mastering the concept of function is of great significance for learning high school mathematics well.