Summing Quadratic Forms in Three Variables: True or False?

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SUMMARY

The statement "The sum of two quadratic forms in three variables must be a quadratic form as well" is true. Quadratic forms can be expressed in matrix notation as x' A x, where A is a symmetric matrix. When summing two quadratic forms, the resulting expression remains a quadratic form due to the properties of matrix addition and linearity. This conclusion is supported by the structure of quadratic forms and their representation in linear algebra.

PREREQUISITES
  • Understanding of quadratic forms and their properties
  • Familiarity with matrix notation and operations
  • Knowledge of linear algebra concepts, particularly symmetric matrices
  • Basic grasp of polynomial functions and their classifications
NEXT STEPS
  • Study the properties of quadratic forms in linear algebra
  • Learn about matrix representation of quadratic forms
  • Explore the implications of summing quadratic forms in higher dimensions
  • Investigate applications of quadratic forms in optimization problems
USEFUL FOR

Students studying linear algebra, mathematicians interested in quadratic forms, and anyone involved in optimization and mathematical modeling.

MikeDietrich
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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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Yes, the answer looks quite trivial...
 
Are you dealing with quadratic forms associated with matrices?

<br /> x&#039; A x<br />

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

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