f ( z ) = ∑ k = 0 ∞ f ( k ) ( z 0 ) k ! ⏟ a k ( z − z 0 ) k {\displaystyle f(z)=\sum _{k=0}^{\infty }\underbrace {\frac {f^{(k)}(z_{0})}{k!}} _{a_{k}}(z-z_{0})^{k}}
