**6.Perpendicular distance from outside point P(x1,y1) ( not lying on a line) on a line x cos ***a* + y sin* a* = p

**is **

**| x₁ cos ***a* + y₁ sin* a* – p | .

**7.To find the point of intersection of two lines—**

Lines must be non-parallel line . Its mean parallel line does not meet .

Suppose , the two lines be

a₁x + b₁y + c₁ = 0. and a₂x + b₂y + c₂ = 0

If (x₁ , y₁ ) be the co-ordinates of their point of intersection—

Then

a₁x + b₁y + c₁ = 0. and

a₂x + b₂y + c₂ = 0

solving these two equation and find ( x , y )

**8.Concurrent lines :**

If three given lines are concurrent they must be meet in a common point.

**Method to find concurrency—**

**Method 1.**

Firstly we find point of intersection on solving any two lines. If this point satisfy the third equation also , the given lines are concurrent.

**Method 2.**

Determinant form

Let three lines a ᵢ x + b ᵢ y + c ᵢ = 0

i = 1 ,2 ,3 are concurrent if