-1\; ]=arctg\frac{3-0,5}{1+3\cdot 0,5}=\\\\=arctg\frac{2,5}{2,5}=arctg1=\frac{\pi}{4}\\\\\\\star \; \; arctgx-arctgy=\left\{\begin{array}{ccc}arctg\frac{x-y}{1+xy}\; ,\; esli\; xy>-1\; ,\\\pi +arctg\frac{x-y}{1+xy}\; ,\; esli\; x<0,\; xy<-1\; ,\\-\pi +arctg\frac{x-y}{1+xy}\; ,\; esli\; x<0,\; xy<-1\end{array}\right" alt="tga=3\; \; ,\; \; tg\beta =-0,5\\\\a\in (0,\frac{\pi }{2})\; ,\; \; \beta \in (-\frac{\pi }{2},0)\\\\a=arctg3\; \; ,\; \; \beta =arctg(-0,5)=-arctg0,5\\\\a+\beta =arctg3-arctg0,5=\Big [\; 3\cdot 0,5=1,5>-1\; ]=arctg\frac{3-0,5}{1+3\cdot 0,5}=\\\\=arctg\frac{2,5}{2,5}=arctg1=\frac{\pi}{4}\\\\\\\star \; \; arctgx-arctgy=\left\{\begin{array}{ccc}arctg\frac{x-y}{1+xy}\; ,\; esli\; xy>-1\; ,\\\pi +arctg\frac{x-y}{1+xy}\; ,\; esli\; x<0,\; xy<-1\; ,\\-\pi +arctg\frac{x-y}{1+xy}\; ,\; esli\; x<0,\; xy<-1\end{array}\right" align="absmiddle" class="latex-formula">