Middle term(s) in $(a+b)^n$ (Even n: single middle term at r=n/2. Odd n: two middle terms r=(n±1)/2.)

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Even n: single middle term at r=n/2. Odd n: two middle terms r=(n±1)/2.

What each symbol means

SymbolWhat it stands for
nExpansion degree

When to use this

Positive integer n.