The value of $\mathrm{cosec}\frac{\mathrm{\pi }}{18}-4\sin \frac{7\mathrm{\pi }}{18}$ is

$\begin{array}{l}\mathrm{cosec}{10}^{\circ }-4\sin {70}^{\circ }\\ =\frac{1-4\sin {70}^{\circ } \sin {10}^{\circ }}{\sin {10}^{\circ }}\\ =\frac{1-2\left(\cos {60}^{\circ }-\cos {80}^{\circ }\right)}{\sin {10}^{\circ }}\\ =\frac{1-2\left(\frac{1}{2}-\sin {10}^{\circ }\right)}{\sin {10}^{\circ }}\\ =\frac{1-1+2\sin {10}^{\circ }}{\sin {10}^{\circ }}=2\end{array}$