Can a Function Be Expressed as the Sum of an Even and an Odd Function?

In summary, the function f can be written as the sum of an even function and an odd function. The even function is g(x) = \frac{f(x)+f(-x)}{2} and the odd function is h(x) = \frac{f(x)-f(-x)}{2}. The equal sign can be written as g+h, and the function can be written as f=g+h.
  • #1
John O' Meara
330
0

Homework Statement


Suppose that the function f has domain all real numbers. Show that f can be written as the sum of an even function and an odd function.


Homework Equations


f(-x) = f(x) is even and f(-x)=-f(x) is odd


The Attempt at a Solution


If g(x) is an even function it can be written as [tex]g(x) = \frac{f(x)+f(-x)}{2} where f(x) is even and if h(x) is odd it can be written as h(x)=\frac{f(x)-f(-x)}{2} [/tex]. but how do you write f = g + h?
 
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  • #2
[tex]
f(x) = \frac{f(x)+f(-x)}{2} + \frac{f(x)-f(-x)}{2}
[/tex]

Now what can you say about [tex] \frac{f(x)+f(-x)}{2}[/tex] and [tex]
\frac{f(x)-f(-x)}{2}[/tex] ?
 
  • #3
John O' Meara said:

Homework Statement


Suppose that the function f has domain all real numbers. Show that f can be written as the sum of an even function and an odd function.


Homework Equations


f(-x) = f(x) is even and f(-x)=-f(x) is odd


The Attempt at a Solution


If g(x) is an even function it can be written as [tex]g(x) = \frac{f(x)+f(-x)}{2}[/tex] where f(x) is even and if h(x) is odd it can be written as h(x)=\frac{f(x)-f(-x)}{2} [/tex]. but how do you write f = g + h?

Your wording is awkward. It is not "if g is an even function then..." and "if h is odd...". You want to define g(x) to be (f(x)+ f(-x))/2 and show that it is even. Define h(x) to be (f(x)- f(-x))/2 and show that it is odd.

[tex]g+h= \frac{f(x)+ f(-x)}{2}+ \frac{f(x)- f(-x)}{2}= \frac{f(x)+ f(-x)+ f(-x)+ f(x)- f(-x)}{2}[/tex]
What is that equal to?
 
  • #4
How did Hallsofivy get five terms in the last equation divided by 2. I would only have got four divided by 2.
 
  • #5
John O' Meara said:
How did Hallsofivy get five terms in the last equation divided by 2. I would only have got four divided by 2.

It looks like a typo. The second [itex]+f(-x)[/itex] shouldn't be there.
 
  • #6
And the answer that those four terms divided by 2 is f(x). Now I am embarrassed asking the question, it is so simple.
 
  • #7
Haha. No worries. That was what VeeEight was getting at as well. It is a neat problem that is just a little trick of dividing by 2. No need to feel embarrassed.
 
  • #8
John O' Meara said:
How did Hallsofivy get five terms in the last equation divided by 2. I would only have got four divided by 2.

n!kofeyn said:
It looks like a typo. The second [itex]+f(-x)[/itex] shouldn't be there.
Yes, my eyes went squoggly for a moment. Thanks, n!kofeyn.
 
  • #9
Thanks all of you for your replies.
 

1. What is a sum of odd and even functions?

A sum of odd and even functions is a mathematical concept where two functions, one being odd and the other being even, are added together to form a new function. These functions have specific properties that make them behave differently when added together.

2. What are the properties of odd and even functions?

An odd function is symmetric about the origin and has the property that f(-x) = -f(x), while an even function is symmetric about the y-axis and has the property that f(-x) = f(x). Additionally, the sum of an odd and even function is always an odd function.

3. How do you determine if a function is odd or even?

To determine if a function is odd or even, you can use the symmetry properties mentioned above. If f(-x) = -f(x), then the function is odd. If f(-x) = f(x), then the function is even. You can also look at the power of the variables in the function, as odd functions typically have an odd power and even functions have an even power.

4. Can you give an example of a sum of odd and even functions?

One example of a sum of odd and even functions is f(x) = x^3 + x^2. The first term, x^3, is an odd function, and the second term, x^2, is an even function. When added together, they form a new function that is odd.

5. What is the importance of understanding sum of odd and even functions?

Understanding sum of odd and even functions is important in various areas of mathematics, such as calculus, differential equations, and Fourier series. These concepts are also used in physics and engineering to model and solve real-world problems. Additionally, they provide a deeper understanding of mathematical symmetry and how functions behave when combined.

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