# Geometric distribution

Keep tossing a coin, how likely to get the first heads at the $k$-th toss?

$p$
$$p(k) = \begin{cases} (1-p)^{k-1}p, & \text{if k = 1, 2, \cdots,} \\\ 0, & \text{otherwise.} \end{cases} \\[16pt] \text{where p is the probability the coin lands on heads.}$$