Binomial Theorem or Binomial Expansion:

$$(x+y)^n = \sum_{k=0}^n {n \choose k} x^{n - k} y^k$$

$$\binom{n}{k}$$

$$P(A \mid B) = \frac{P(B \mid A) \, P(A)}{P(B)}$$

Inclusion–exclusion principle:

$$|A \cup B \cup C| = |A| + |B| + |C| - |A \cap B| - |A \cap C| - |B \cap C| + |A \cap B \cap C|$$

$$\frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$

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