Two nonvertical lines have slopes m₁ and m₂, respectively.

The lines are parallel if _____

and the_______ are unequal; the line are perpendicular if______

The lines are parallel if _____

and the_______ are unequal; the line are perpendicular if______

m₁ = m₂and they-interceptsare unequal; the lines are perpendicular if(m₁)(m₂)=–1.