Tuesday, October 25, 2016

Linear Equation of Two Variables, sum of straight lines

Students reading in class IX and X can send mathematics , which they are  not able to understand or  grasp, send an email with the mathematics at

kaacconsultant@gmail.com

that math will appear in this blog which will help others also







Two liner equation, both represents straight line

          a1 x + b1 y + c1 =    0
and     a2 x + b2 y +c2 =    0

Both the equation represents  two straight lines

General equation of an straight line    Y= M X +  C  where M is the inclination to the vertical axis called  gradient or slope and  C is the point where the line intersects with vertical  axis.


If we try to rearrange the equations in Y= MX + C form


a1x + b1y +c1 = 0
or ,    b1y  = -a1x - c1
or          y = -a1/b1 x  - c1/b1

Now the equation took the shape of  Y = MX +C

so     M= -a1/b1
and   C = -c1/b1





Suppose two linear equation are as follows

 6x-2y +9 = 0          ------------    1
3x -  y +12  = 0        ------------   2

equation 1      6x -2y +9 = 0
                     or,  -2y = -6x -9
                     or      y =  -6/-2 x  -9/-2
                     or      y = 3 x +9/2


From equation 1  slope or gradient value is  3

For  equation 2,   3x - y + 12 =0
                          or   -y = -3x -12
                          or    y =   3x +12

In this equation slope or gradient is  also 3

So both the equations gradient is same  so the lines are parallel.

When two lines are parallel , both the lines can not intersect at a common point. So the intersection point is unreal.


In the other example
Two equations are      2x +3y -2 = 0 ------------- 1
                                    x  - 2y  - 8 = 0  ------------2


slopes or gradients are     2x +3y -2 = 0

                                       or,   3y =   -2x +2
                                       or,     y =  -2/3 x + 2/3

so     slop is   -2/3

For second equation         x -2y -8 = 0

                                     or,   -2y =   -x +8

                                      or      y =  1/2 x  - 8/2

so slop of the second line is  1/2

When both the lines slope that is angle of inclination or gradient is different  the lines will intersect at a common point

Now if we  try to solve the equation we will get the point of intersection that is at the point of intersection both the equation  is satisfied


From first equation    y =  -2/3 x  + 2/3

From second equation y= 1/2 x  -  8/2

if the value of  y  is put   in equation 1

                            1/2 x  -8/2 = -2/3 x  + 2/3

                         or, 1/2 x + 2/3 x =   2/3 + 4
                         or, x = 4

Putting x =4 ,
 y = 1/2*4 - 4
or y =   -2                      So the point of intersection  (4,-2 )


Now in other conditions , let two lines are coincidence that is one line is lying on other , then how come the equations are different, It happens , when one line length is bigger or shorter than the other line.

Two equations are  5x -15y = 8 ------------ 1
other equation is     3x - 9y  = 24/5 -----------2

slope or gradient will be same and simultaneously   intersection point with the vertical axis will also be the same
                               rearranging the lines in y= mx +c pattern
                     
                                                                    5x -15 y = 8
                                                             or,       -15 y =  -5x +8
                                                             or,             y=  1/3 x - 8/15

 For other equation                                       3x -9y = 24/5
                                                              or,        -9y = -3x + 24/5
                                                              or,           y =  1/3 x - 8/15


So for both the equations  slope and intersection point at the vertical axis  are same . So both the lines are coincidence.





Now another interesting aspect
If the equation        x  =  a   this is also an equation of a straight line  which is parallel to vertical y axis

Similarly if the equation is  y = b , this straight line is parallel to  horizontal x axis. .

this both straight lines will met at the intersection point at (a,b)

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