The value of $\cosec\dfrac{\pi}{18}-\sqrt{3} \sec \dfrac{\pi}{18}$ is a-

$\tan \theta=p \text { হলে, } \cos 2 \theta=\text { কত? }$

$\frac{1+\tan 25^{\circ}}{1-\tan 25^{\circ}}=$ কত?

sin (A-30°) + sin (150°+A) এর মান-

The value of $\sum\limits_{r = 1}^9 {{{\sin }^2}\dfrac{{\pi r}}{{18}}} \;is\;equal\;to\;$