# What is the opposite of a cross term?

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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I'm not aware of standard terminology, but I'd call them "pure terms". –  Matt Pressland Mar 28 '12 at 13:15
The happy terms?! –  Ross Millikan Mar 28 '12 at 13:21
The "non-cross" terms? –  David Mitra Mar 28 '12 at 13:26

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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+1, Came here to give this answer. I think I have seen diagonal used most often. –  Eric Naslund Mar 28 '12 at 13:29

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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