1/sin170° - /sin 100° чему равно значение выражения

Решите задачу:

$\frac{1}{sin170^\circ }-\frac{\sqrt3}{sin100^\circ} = \frac{1}{sin(180-10)}-\frac{\sqrt3}{sin(90+10)} = \frac{1}{sin10} -\frac{\sqrt3}{cos10} =\\\\= \frac{cos10-\sqrt3\cdot sin10}{sin10\cdot cos10} =\frac{cos10-tg60\cdot sin10}{\frac{1}{2}sin20} = \frac{cos10-\frac{sin60}{cos60}\cdot cos10}{\frac{1}{2}sin20} =\\\\= \frac{2\cdot (cos60\cdot cos10-sin60\cdot sin10)}{cos60\cdot sin20} = \frac{2\cdot cos(60+10)}{\frac{1}{2}\cdot sin(90-70)}= \frac{4\cdot cos70}{cos70} =4$