**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 ai x + bi y + c i = 0**

**i = 1 ,2 ,3 are concurrent if**