Checkpoint 9 Answer

Since the derivative of erf` text[(] t text[)]` is `(2e^(-t^2))/sqrt(pi)`, the Fundamental Theorem of Calculus tells us that

erf` text[(] t text[)] =` erf` text[(] t text[)] -` erf` text[(] 0 text[)] = int_0^t (2e^(-s^2))/sqrt(pi) ds`.