$\sec \theta=\frac{5}{2}$ হলে, $\operatorname{cosec} \theta$ এর মান কোনটি?

$\frac{2}{\sqrt{30}}$

$\frac{2}{\sqrt{30}}$

$\frac{-\sqrt{21}}{5}$

$\frac{5}{\sqrt{21}}$