Let me try again

Let me make a test
This is an inline math :$\sum_{i=1}^nx_iy_i\leq\sqrt{\sum_{i=1}^nx_i}\sqrt{\sum_{i=1}^n y_i}$
This is in display math: $$\sum_{i=1}^nx_iy_i\leq\sqrt{\sum_{i=1}^nx_i}\sqrt{\sum_{i=1}^n y_i}$$
New line
\[\sum_{i=1}^nx_iy_i\leq\sqrt{\sum_{i=1}^nx_i}\sqrt{\sum_{i=1}^n y_i}\]

$\begin{tabular}{c|c|c}a&b&c\\d&e&f\end{tabular}$