Categorie: Tutti - theorem - functions - polynomial - continuity

da David Kedrowski mancano 14 anni

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MAT.126 1.4-1.5

The study of continuity and one-sided limits involves understanding how functions behave at every point within their domain. Key concepts include the properties of continuity, which apply to various types of functions, such as polynomial, rational, radical, and trigonometric.

MAT.126 1.4-1.5

MAT.126 1.4-1.5

1.5 Infinite Limits

Find and sketch the vertical asymptotes of the graph of a function

If f(x) approaches infinity (or negative infinity) as x approaches c from the right or the left, then the line x=c is a vertical asymptote of the graph of f.

Subtopic
Theorem 1.14 Vertical Asymptotes

Let f and g be continuous on an open interval containing c. If f(c) is not zero, g(c) is zero, and there exists an open interval containing c such that g(x) is not 0 for all x not c in the interval, then the graph of the function given by

h(x) = f(x) / g(x)

has a vertical asymptote at x=c.

Determine infinite limits from the left and from the right

Let f be a function that is defined at every real number in some open interval containing c (except possibly at c itself).

The statement the limit of f(x) as x approaches c equals positive infinity means that for each M>0 there exists a delta>0 such that f(x)>M whenever 0<|x-c|<delta.

The statement the limit of f(x) as x approaches c equals negative infinity means that for each N<0 there exists a delta>0 such that f(x)<N whenever 0<|x-c|<delta.

To define the infinite limit from the left, replace 0<|x-c|<delta by c-delta<x<c.

To define the infinite limit from the right, replace 0<|x-c|<delta by c<x<c+delta.

1.4 Continuity and One-Sided Limits

Understand and use the Intermediate Value Theorem
Theorem 1.13 Intermediate Value Theorem

If f is continuous on the closed interval [a,b], f(a) is not equal to f(b), and k is any number between f(a) and f(b), then there is at least one number c in [a,b] such that f(c)=k.

The method of bisection depends on the intermediate value theorem and therefore on the continuity of polynomials (and other functions).

This is an example of an existence theorem, a theorem that states that something exists but does not provide a method for finding that which does exit.

Use properties of continuity
Theorem 1.12 Continuity of a Composite Function
Functions Continuous At Every Point in Their Domain

Polynomial

Rational

Radical

Trigonometric

Theorem 1.11 Properties of Continuity

See your text, p. 75

Determine one-sided limits and continuity on a closed interval
Continuity on a Closed Interval

A function f is continuous on the closed interval [a,b] if it is continuous on the open interval (a,b) and the limit from the right of f(x) as x approaches a is equal to f(a) and the limit from the left of f(x) as x approaches b is equal to f(b).

The function f is continuous from the right at a and continuous from the left at b.

Theorem 1.10 The Existence of a Limit

Let f be a function and let c and L be real numbers. The limit of f(x) as x approaches c is L if and only if the limit from the left of f(x) as x approaches c is L and the limit from the right of f(x) as x approaches c is L.

One-sided Limits

Limit from the left

Also called a left-hand limit.

Refers to a limit where x approaches c only from values less than c (to the left of c on a number line or on the x-axis).

Limit from the right

Also called a right-hand limit.

Refers to a limit where x approaches c only from values greater than c (to the right of c on a number line or on the x-axis).

Determine continuity at a point and continuity on an open interval
Discontinuities

Consider a function f, defined on an open interval I containing c (except possibly at c). This function is said to be discontinuous at c if any one of the following are true:


  • The function f is not defined at x=c.
  • The limit of f(x) does not exist at x=c.
  • The limit of f(x) exists at x=c, but it is not equal to f(c).
  • Nonremovable

    A discontinuity at c is called nonremovable if f cannot be made continuous by appropriately defining (or redefining) f(c).

    Removable

    A discontinuity at c is called removable if f can be made continuous by appropriately defining (or redefining) f(c).

    Continuity: Formal

    On an Open Interval

    A function is continuous on an open interval (a,b) if it is continuous at each point in the interval.

    A function that is continuous on the entire real line is everywhere continuous.

    At a Point

    A function f is continuous at c if the following three conditions are met.

    1. f(c) is defined.

    2. The limit of f(x) as x appraches c exists.

    3. The function value and the limit value are equal.

    Continuity: Informal

    To say that a function f is continuous at x=c means that there is no interruption in the graph of f at c.

    That is, its graph is unbroken at c and there are no holes, jumps, or gaps.