Symmetry ${}^n C_r = {}^n C_{n-r}$ (Choosing r is same as leaving n−r: nCr = nC(n−r))

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Choosing r is same as leaving n−r: nCr = nC(n−r)

What each symbol means

SymbolWhat it stands for
n,rIntegers 0≤r≤n

When to use this

Standard binomial coefficients.