Binomial Expansions

Binomial Expansions
(a+b)^n = a^n + \dbinom{n}{1}a^{n-1} b + \dbinom{n}{2}a^{n-2} b^2 + ...
+ \dbinom{n}{r}a^{n-r} b^r + ... +  b^{n}
General Term
T_{r+1}=\dbinom{n}{r}a^{n-r} b^r
\dbinom{n}{r}=\dfrac{n!}{r!(n-r)!} = \dfrac{n(n-1)...(n-r+1)}{r!}
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