In lower classes, we studied the basic concept of coordinate geometry, like distance formula, section - formula, area of triangle and slope of a straight lines etc.

**System of straight lines**

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**1. Recall**

In lower classes, we studied the basic concept of coordinate geometry, like distance formula, section - formula, area of triangle and slope of a straight lines etc.

We also studied various form of equations of lines in X std. Let us recall the equations of straight lines. Which will help us for better understanding the new concept and definitions of XI std co-ordinate geometry.

**Various forms of straight lines:**

**i. Slope-intercept form**

Equation of straight line having slope *m* and *y*-intercept ‘*c*’ is *y* = *mx*+*c*

**ii. Point- slope form**

Equation of Straight line passing through the given point *P* (*x*1 , *y*1) and having a slope *m* is

**iii. Two-Point form**

**i. Intercept form**

**ii. General form**

Equation of straight line in general form is *ax* + *by* + *c* = 0 where *a*, *b* and *c* are constants and *a*, *b* are not simultaneously zero.

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**2. Angle between two straight lines**

Let *l*1 and *l*2 be two straight lines represented by the equations *l*1: *y* = *m*1 *x* + *c*1 and *l*2:* y *=* m*2* x *+* c*2* *intersecting at* P*.

If *θ*1 and *θ* 2 are two angles made by *l*1 and *l*2 with *x*- axis then slope of the lines are *m*1* *=* *tan* **θ* 1* *and* m*2* *=* *tan* **θ* 2* *.

From fig 3.3, if *i* is angle between the lines *l*1* *&* l*2* *then

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**3. Distance of a point from a line**

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**4. Concurrence of three lines**

If two lines *l*1 and l2* *meet at a common point* P*, then that* P *is called point of* *This intersection of *l*1 and *l*2 . point of intersection is obtained by solving the equations of *l*1 and *l*2 .

If three or more straight lines will have a point in common then they are said to be concurrent.

The lines passing through the common point are called concurrent lines and the common point is called concurrent point.

**Conditions for three given straight lines to be concurrent**

Tags : Definition, Formula, Solved Example Problems, Exercise | Mathematics , 11th Business Mathematics and Statistics(EMS) : Chapter 3 : Analytical Geometry

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11th Business Mathematics and Statistics(EMS) : Chapter 3 : Analytical Geometry : System of straight lines | Definition, Formula, Solved Example Problems, Exercise | Mathematics