[tex]k:\ y=m_1x+b_1\ \ \ and\ \ \ l:\ y=m_2x+b_2\\\\k\perp l\ \ \ \Leftrightarrow\ \ \ m_1\cdot m_2=-1\\------------------------\\\\k:\ y=2x+13\ \ \ \ and\ \ \ \ l:\ y=m_2x+b_2\\\\2\cdot m_2=-1\ \ \ \Leftrightarrow\ \ \ m_2=- \frac{1}{2} \\\\l:\ y=- \frac{1}{2} x+b_2\ \ \ and\ \ \ b_2\ \in\ R\\\\for\ example:\\\\y=- \frac{1}{2} x,\ \ \ y=- \frac{1}{2} x+5 \frac{1}{7} ,\ \ \ y=- \frac{1}{2}x - \sqrt{13}\ ,\ ...[/tex]