Пожалуйста помогите решить tg225-tg195=?

Решите задачу:

$tg225-tg195=tg(\pi+45)-tg(\pi+15)=tg45-tg15=\\=\frac{\sin(45-15)}{\cos45\cos15}=\frac{\sin30}{\cos45\cos15}\\\cos45\cos15=\frac{\cos(45-15)+\cos(45+15)}2=\frac{\cos30+\cos60}2=\frac{\frac{\sqrt3}2+\frac12}2=\frac{\sqrt3+1}4\\\frac{\sin30}{\cos\left(\pi+45\right)\cos\left(\pi+15\right)}=\frac12:\frac{\sqrt3+1}4=\frac12\cdot\frac4{\sqrt3+1}=\frac2{\sqrt3+1}$