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MATHEMATICS - THEORY

    Function


The quantity relationship of
function y = x2 + x + 1

 

If the quantity of y is determined by another value x, then y is a function of x. If f denotes the function, then the formula y = f(x) indicate y depends on x. Thus y is a dependent variable and x is a independent variable. An example of a function would be:

     y = x2 + x + 1

The diagram on the left shows that the quantity of y which is equal to x2 + x + 1 depends on the value of x.

 

 

  Limit of a Function

   

If for each positive ε, no matter how small, there is a corresponding positive δ such that if

     

then

     

In this situation, the limit of f(x) is A as x approaches a, and it can be written as:

     

     
    Limits Involving Infinity

In this segment, three kind of situations will be discussed.
     

The limit of f(x) is infinity
when x approaches 1
 
  • The limit of f(x) is ∞ as x approaches a if for each number B, no matter how large, there is a corresponding positive δ, such that if

       

then

     f(x) > B

Its notation is

     

     

The limit of f(x) is 1
when x approaches +∞
 
  • The limit of f(x) is A as x approaches ∞ if for each positive ε, no matter how small, there is a corresponding B such that if

       x > B

then

     

Its notation is

     

     

The limit of f(x) is -∞ when x
approaches -∞
 
  • The limit of f(x) is -∞ as x approaches -∞ if for each number B, no matter how large, there is a corresponding C, such that if

       x< -C

then

     f(x) < -B

Its notation is

     

     

Summary
  Summary

  This section introduces limit of a function and three cases involving infinity. When discussing limit of a function, it must be the limit of a specific point.