Let $\ $ ${y_1\cdot...\cdot y_n} \in \mathbb{R}$ $\ $ be positive $\quad$
Prove: $\sqrt[n]{y_1\cdot...\cdot y_n}$ $\le$ $\frac{y_1+...+y_n}{n}$
I have tried to find this by searching keywords like gemometric and arithmetic average, but hadn't found.
Actually, I have no idea how to start proving this one.