# Gamma gamma gameleon

Calculus Level 3

Which of the following is/are used in the derivation of

$(s-1)! \equiv \int_{0}^{\infty} e^{-t}t^{s-1} \, dt?$

$$\quad \text{A: Integration by parts} \\ \quad \text{B: U-substitution} \\ \quad \text{C: Induction}$$

×