SOLUTION: Find the constant m for which all three lines 2x - y - 4 = 0 , x + 2y + 3 = 0 and mx + y - 1 = 0 intersect at one point. Note: Can you please show your full solution? Thank yo

Algebra ->  Points-lines-and-rays -> SOLUTION: Find the constant m for which all three lines 2x - y - 4 = 0 , x + 2y + 3 = 0 and mx + y - 1 = 0 intersect at one point. Note: Can you please show your full solution? Thank yo      Log On


   



Question 1180577: Find the constant m for which all three lines 2x - y - 4 = 0 , x + 2y + 3 = 0 and mx + y - 1 = 0 intersect at one point.
Note: Can you please show your full solution? Thank you!

Found 2 solutions by ikleyn, MathLover1:
Answer by ikleyn(52782) About Me  (Show Source):
You can put this solution on YOUR website!
.
Find the constant m for which all three lines 2x - y - 4 = 0 , x + 2y + 3 = 0 and mx + y - 1 = 0 intersect at one point.
Note: Can you please show your full solution? Thank you!
~~~~~~~~~~~~~


First, solve the system to find the coordinates of the intersection point.


    2x - y =  4    (1)

    x + 2y = -3    (2)


I will solve by the Substitution method.

From equation (1), express  y = 2x - 4 and substitute this expression into equation (2)


    x + 2*(2x-4) = -3

    x + 4x - 8 = -3

        5x     = -3 + 8 = 5

         x              = 5/5 = 1


Then y = 2x-4 = 2*1 - 4 = 2 - 4 = -2.


Thus the solution to the system is  (x,y) = (1,-2);  so, the intersection point is (1,-2).


    
    Ok, we just solved half of the problem.

    Now our goal is to find  "m"  in the last equation.



For it, substitute the found coordinates of the intersection point  x= 1,  y= -2  into the equation

    m*1 + (-2) -1 = 0,


which gives the ANSWER  m = 3.

Solved, explained, and full solution is shown, step by step in all details.


Have a nice day (!)



Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!


2x+-+y+-+4+=+0.............eq.1
x+%2B+2y+%2B+3+=+0 .............eq.2
mx+%2B+y+-+1+=+0.............eq.3
---------------------------------------
start with
2x+-+y+-+4+=+0.............eq.1
x+%2B+2y+%2B+3+=+0 .............eq.2...........both sides multiply by 2
--------------------------------
2x+-+y+-+4+=+0.............eq.1
2x+%2B+4y+%2B+6+=+0 .............eq.2.............subtract
--------------------------------------------
2x+-+y+-+4-%282x+%2B+4y+%2B+6%29+=+0
2x+-+y+-+4-2x+-+4y+-+6+=+0
-+5y+-+10+=+0
+-+10+=+5y
y=-10%2F5
y=-2

go to
2x+-+y+-+4+=+0.............eq.1, substitute y
2x+-+%28-2%29+-+4+=+0
2x+%2B2+-+4+=+0
2x++-+2+=+0
2x++=+2
x=1

go to
mx+%2B+y+-+1+=+0.............eq.3, substitute x and y
m%2A1+-2+-+1+=+0
m+-3+=+0
m++=+3
third line is
3x+%2B+y+-+1+=+0
all three lines intersect at point (1,-2)
+graph%28+600%2C+600%2C+-10%2C+10%2C+-10%2C+10%2C+-3x%2B1%2C2x-4%2C-x%2F2-3%2F2%29+