- If m₁
** ** = m₂

Both lines are parallel to each other.

θ = 0

2. If m₁m₂ = -1

Both lines are parallel to each other.

θ = 90

Two given line –

L₁ :: a₁x + b₁y + c₁ = 0 and

L₂ :: a₂x + b₂y + c₂ = 0

Parallel Test :

If a₁ : a₂ = b₁ : b₂ ( both slope are equal m₁ = m₂ )

Perpendicular Test :

If a₁a₂+ b₁b₂ = 0 ( m₁m₂ = -1 )

Identical Test :

a₁ : a₂= b₁:b₂ = c₁:c₂