[tex]l_1:\; \; y_1=\sqrt3\, x+\frac{1}{\sqrt3}\; \; ,\qquad l_2:\; y_2=-\frac{1}{\sqrt3}\, x-\sqrt3\\\\\\k_1=\sqrt3\; ,\; \; k_2=-\frac{1}{\sqrt3}\\\\k_1\cdot k_2=\sqrt3\cdot (-\frac{1}{\sqrt3})=-1\; \; \; \; \Rightarrow \; \; \; \; \; l_1\perp l_2\; ,\; \; \underline {\; \angle (l_1,l_2)=90^\circ \; }[/tex]