If lines are perpendicular to each other then \({m_1} \times {m_2} = - 1\) conversely if \({m_1} \times {m_2} = - 1\) then the lines are perpendicular to each other.

Constructions (accurate drawings) can be made using a ruler, a pair of compasses and a pencil. A line which cuts an angle into two equal side angles is called an angle bisector. In geometry a ...