Summing Quadratic Forms in Three Variables: True or False?

In summary, the question of whether the sum of two quadratic forms in three variables must also be a quadratic form is being discussed. The given equation is q(x_1,x_2,x_3)=x_1^2+x_2^2+x_3^2+x_1x_3+x_2x_3. The initial attempt at a solution reveals that the statement seems obvious, but there may be more to it when dealing with quadratic forms associated with matrices. Further discussion and clarification may be needed to fully answer the question.
  • #1
MikeDietrich
31
0

Homework Statement


True or False and Why?

"The sum of two quadratic forms in three variables must be a quadratic form as well."


Homework Equations


q(x_1,x_2,x_3)=x_1^2+x_2^2+x_3^2+x_1x_3+x_2x_3



The Attempt at a Solution


I am definitely missing something. To me this is a "duh" statement (and I am sure it's not). If I sum two equations in quadratic form then naturally the answer will be in the quadratic form. Any hints appreciated.
 
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  • #2
Yes, the answer looks quite trivial...
 
  • #3
Are you dealing with quadratic forms associated with matrices?

[tex]
x' A x
[/tex]

If so, you probably need to take that into account.
 

1. What is a quadratic form?

A quadratic form is a mathematical expression that involves terms of degree two, such as ax2 + bx + c. It is used to represent a function or equation in two or more variables.

2. How is a quadratic form different from a quadratic equation?

A quadratic form is a general expression that can represent a variety of functions, while a quadratic equation is a specific type of function that has one variable squared and can be solved for a specific value. Quadratic forms can have multiple variables and can be used to represent a range of equations.

3. What is the purpose of using a quadratic form?

Quadratic forms are useful in many areas of mathematics, including optimization, calculus, and linear algebra. They can also be used in physics and engineering to model real-world situations such as motion and forces.

4. How is a quadratic form related to a matrix?

A quadratic form can be represented by a matrix called a quadratic form matrix. This matrix contains the coefficients of the quadratic terms and can be used to simplify calculations and solve equations involving the quadratic form.

5. Can quadratic forms have negative or non-integer coefficients?

Yes, quadratic forms can have negative or non-integer coefficients. They can also have higher degree terms, although they are still referred to as quadratic forms. These variations can be seen in more complex equations and have important applications in mathematics and other fields.

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