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Sum of a Binomial Expansion
## Formula
From:
$$(1+x)^n=\sum_{k=0}^{n}\binom nkx^k$$
putting:
$$x=1$$
gives:
$$\sum_{k=0}^{n}\binom nk=2^n$$
Putting:
$$x=-1$$
gives:
$$\sum_{k=0}^{n}(-1)^k\binom nk=0$$
for:
$$n\ge1$$
## Usage
- Used to evaluate binomial coefficient sums quickly.
