$$a=\frac{1}{sin40}-\frac{\sqrt3}{cos40}$$ olsun.
$$a=\frac{cos40-\sqrt3.sin40}{sin40.cos40}$$
$$a=\frac{cos40-\frac{sin60}{cos60}.sin40}{\frac{sin80}{2}}$$
$$a=\frac{cos40.cos60-sin60.sin40}{\frac{cos60.sin80}{2}}$$
$$a=4.\frac{cos(100)}{sin80}=-4\frac{cos(80)}{sin80}=-4cot80$$