“limit”的意思、由来-百科全书

limit

mathematics

mathematical concept based on the idea of closeness, used primarily to assign values to certain functions (function) at points where no values are defined, in such a way as to be consistent with nearby values. For example, the function (x²− 1)/(x− 1) is not defined when x is 1, because division by zero is not a valid mathematical operation. For any other value of x, the numerator can be factored and divided by the (x− 1), giving x+1. Thus, this quotient is equal to 2 for all values of x except 1, which has no value. However, 2 can be assigned to the function (x²− 1)/(x− 1) not as its value when x equals 1 but as its limit when x approaches 1. See analysis: Continuity of functions (analysis).

One way of defining the limit of a function f(x) at a point x₀, written as

is by the following: if there is a continuous (continuity) (unbroken) function g(x) such that g(x)=f(x) in some interval around x₀, except possibly at x₀ itself, then

The following more-basic definition of limit, independent of the concept of continuity, can also be given:

if, for any desired degree of closeness ε, one can find an interval around x₀ so that all values of f(x) calculated here differ from L by an amount less than ε (i.e., if |x− x₀|\\<δ, then |f (x)− L|\\<ε). This last definition can be used to determine whether or not a given number is in fact a limit. The calculation of limits, especially of quotients, usually involves manipulations of the function so that it can be written in a form in which the limit is more obvious, as in the above example of (x²− 1)/(x− 1).

Limits are the method by which the derivative, or rate of change, of a function is calculated, and they are used throughout analysis as a way of making approximations into exact quantities, as when the area inside a curved region is defined to be the limit of approximations by rectangles.

词条	limit
释义	limit mathematics mathematical concept based on the idea of closeness, used primarily to assign values to certain functions (function) at points where no values are defined, in such a way as to be consistent with nearby values. For example, the function (x²− 1)/(x− 1) is not defined when x is 1, because division by zero is not a valid mathematical operation. For any other value of x, the numerator can be factored and divided by the (x− 1), giving x+1. Thus, this quotient is equal to 2 for all values of x except 1, which has no value. However, 2 can be assigned to the function (x²− 1)/(x− 1) not as its value when x equals 1 but as its limit when x approaches 1. See analysis: Continuity of functions (analysis). One way of defining the limit of a function f(x) at a point x₀, written as is by the following: if there is a continuous (continuity) (unbroken) function g(x) such that g(x)=f(x) in some interval around x₀, except possibly at x₀ itself, then The following more-basic definition of limit, independent of the concept of continuity, can also be given: if, for any desired degree of closeness ε, one can find an interval around x₀ so that all values of f(x) calculated here differ from L by an amount less than ε (i.e., if \|x− x₀\|\\<δ, then \|f (x)− L\|\\<ε). This last definition can be used to determine whether or not a given number is in fact a limit. The calculation of limits, especially of quotients, usually involves manipulations of the function so that it can be written in a form in which the limit is more obvious, as in the above example of (x²− 1)/(x− 1). Limits are the method by which the derivative, or rate of change, of a function is calculated, and they are used throughout analysis as a way of making approximations into exact quantities, as when the area inside a curved region is defined to be the limit of approximations by rectangles.
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