[tex]The\ slope-intercept\ form:y=mx+b\\\\k:y=m_1x+b_1\ and\ l:y=m_2x+b_2\\\\k\perp l\iff m_1\cdot m_2=-1\Rightarrow m_2=-\frac{1}{m_1}\\-----------------------\\therefore\\a)\ m_1=\frac{1}{2};\ m_2=-\frac{1}{2}\ \boxed{NOT\ :(}\\\\b)\ m_1=5;\ m_2=-\frac{1}{5}\ \boxed{YES\ :)}\ \ 5\cdot(-\frac{1}{5})=-1\\\\c)\ m_1=\frac{1}{5};\ m_2=\frac{1}{5}\ \boxed{NOT\ :(}\\\\d)\ m_1=3;\ m_2=6\ \boxed{NOT\ :(}[/tex]
