1. about cyclic group

how to prove:

C_a * C_b is cyclic when a,b coprime

2. Originally Posted by szpengchao
how to prove:

C_a * C_b is cyclic when a,b coprime
Prove that $(x,y)$ generates $C_a\times C_b$ where $x$ generates $C_a$ and $y$ generates $C_b$.