3.155. $\operatorname{tg} 255^{\circ}-\operatorname{tg} 195^{\circ}$. 

 

The translation of the above text into English, retaining the original text's line breaks and format, is as follows:

3.155. $\operatorname{tg} 255^{\circ}-\operatorname{tg} 195^{\circ}$.
## Solution.

$$
\begin{aligned}
& \tan 255^{\circ}-\tan 195^{\circ}=\tan\left(270^{\circ}-15^{\circ}\right)-\tan\left(180^{\circ}+15^{\circ}\right)= \\
& =\cot 15^{\circ}-\tan 15^{\circ}=\frac{\cos 15^{\circ}}{\sin 15^{\circ}}-\frac{\sin 15^{\circ}}{\cos 15^{\circ}}=\frac{\cos ^{2} 15^{\circ}-\sin ^{2} 15^{\circ}}{\sin 15^{\circ} \cos 15^{\circ}}= \\
& =\frac{\cos 30^{\circ}}{\sin 15^{\circ} \cos 15^{\circ}}=\frac{2 \cos 30^{\circ}}{2 \sin 15^{\circ} \cos 15^{\circ}}=\frac{2 \cos 30^{\circ}}{\sin 30^{\circ}}=2 \cot 30^{\circ}=2 \sqrt{3} .
\end{aligned}
$$

Answer: $2 \sqrt{3}$.