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When we multiply out $(x + y)(x + y)$, we refer to the two $xy$ terms as "cross terms". Is there a corresponding term for the $x^2$ and $y^2$ terms?

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    $\begingroup$ I'm not aware of standard terminology, but I'd call them "pure terms". $\endgroup$
    – mdp
    Mar 28, 2012 at 13:15
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    $\begingroup$ The happy terms?! $\endgroup$ Mar 28, 2012 at 13:21
  • $\begingroup$ The "non-cross" terms? $\endgroup$ Mar 28, 2012 at 13:26

6 Answers 6

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Depending on the context, "diagonal terms" might work:

$$(x+y)(x+y)=\pmatrix{x&y}\pmatrix{1&1\\1&1}\pmatrix{x\\y}\;;$$

the cross-terms are the off-diagonal terms in this quadratic form and the other ones are the diagonal terms.

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  • $\begingroup$ +1, Came here to give this answer. I think I have seen diagonal used most often. $\endgroup$ Mar 28, 2012 at 13:29
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Direct or straight might be what you are looking for, as opposed to cross, crossed or mixed (since each resultant term has either one variable to a power or two different variables, a "mixture").

I was also taught that you can multiply $(a+b)(c+d)$ using the acronym FOIL for First, Inside, Outside, Last (which is mixing sequential and spatial metaphors).

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The squares or more general, the $n$th power.

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The aligned terms. ............

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The univariate terms is unambiguous. I like 'pure' but am not sure how correct this is.

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The square term or quadrature term is the best.

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