Modular Exponentiation Give numbers $x,y,z$ such that $y \equiv z \pmod{5}$ but $x^y \not\equiv x^z \pmod{5}$  
I'm just learning modular arithmetic and this questions has me puzzled. Any help with explanation would be great!

Take $x=2$, $y=3$, $z=8$. Then $x^y \bmod 5 = 3$ but $x^z \bmod 5 = 1$.
