$$\cos(z)$$ can be expressed as

A

$$\frac{1}{2} (e^{iz}+e^{-iz})$$

B

$$\frac{1}{2} (e^{iz}-e^{-iz})$$

C

$$\frac{1}{2i} (e^{iz}+e^{-iz})$$

D

$$\frac{1}{2i} (e^{iz}-e^{-iz})$$