Domain of a Function: Real vs Complex Numbers

In summary, the domain, codomain, and range of the function f(x) = 2x+1 is the set of all real numbers. However, it could also be the set of all complex numbers, as shown by the example of x = 3+4i and f(x) = 7+8i. Some textbooks may default to the set of real numbers if they have not covered complex numbers, but it should be stated somewhere in the textbook. The range and domain can also be complex numbers, specifically a+bi where b=0. The presentation of the problem may provide a clue to the author's intended domain.
  • #1
davon806
148
1

Homework Statement


Consider some simple single-variable function such as
f(x)=2x+1
The domain,codomain and range of the above function is set of all real numbers.
But why not the set of all complex numbers?
if x = 3+4i
f(x) = 6+8i + 1 = 7+8i,so it is possible for x to be a complex no?


Homework Equations





The Attempt at a Solution

 
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  • #2
If your textbook has not dealt with complex numbers, then the "default" number system is the set of real numbers. It really should be stated somewhere in your textbook, perhaps in the preface of first chapter, but not necessary with each problem.
 
  • #3
My book has mentioned complex no before,but the author still wrote down the domain is the set of all real numbers instead of complex numbers.
 

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  • #4
The range and domain are complex numbers a+bi for which b=0. Your function uses only Real Numbers.
 
  • #5
That means the range and domain of this function are the set of complex number?
 
  • #6
You attached an image of the problem solutions. How is the problem presented? There might be a clue that the author intended the domain to be the reals.
 

FAQ: Domain of a Function: Real vs Complex Numbers

1. What is the difference between a real and complex number?

A real number is a number that can be represented on a number line and includes all rational and irrational numbers. A complex number is a number that consists of a real part and an imaginary part, usually written in the form a + bi, where a and b are real numbers and i is the imaginary unit (√-1).

2. How is the domain of a function affected by real and complex numbers?

The domain of a function is the set of all possible input values, and it can be affected by the type of numbers used in the function. For a function with real numbers, the domain will be all real numbers. For a function with complex numbers, the domain will be all complex numbers.

3. Can a function have both real and complex numbers in its domain?

Yes, a function can have both real and complex numbers in its domain. This is common in functions that involve both real and imaginary components, such as trigonometric functions.

4. How do we determine the domain of a function with complex numbers?

To determine the domain of a function with complex numbers, we must consider the restrictions on the input values. For example, if the function contains a square root of a negative number, then the domain will be restricted to complex numbers. Also, if the function involves division by zero, the domain will be restricted to exclude the value that makes the denominator zero.

5. Can a function with a real number domain be extended to include complex numbers?

Yes, a function with a real number domain can be extended to include complex numbers by defining the function in terms of complex variables. This is often done in mathematics to simplify calculations and solve more complex problems.

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