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Carefully follow the steps to find the solution to the three equation system.
1.2x+y+3:= 12
2. x-2y+z=-5
3.5.x- y+ 2z = 5

a. Use equations 2 and 3 and eliminate the z by multiplication and addition, creating a new equation with only two variables.
b. Use equations 1 and 2 and eliminate the z by multiplication and addition, creating a second equation with only two variables.
c. Use the two new equations, and eliminate the x-variable by multiplication and addition, finding the value for the y-variable.
d. Substitute y-value in the second new equation and find the x-value.
e. Substitute the z-and y-values into original equation 2 to find the z-value

Respuesta :

rspill6

Answer:

This answer assumes that the first equation is meant to read:

2x + y +3z = 12, and not

1.22x+y+3:= 12

Spoiler Alert:  x = 1, y=4, and z=2

Step-by-step explanation:

1.    2x + y +3z = 12

2.     x - 2y + z = -5

3.    5x - y+ 2z = 5

==============

Use equations 2 and 3 to eliminate z:

2.  x - 2y + z= -5

3.  5x - y+ 2z = 5

-2(x - 2y + z) = -2(-5)   [Multiply equation 2 by -2]

             5x -   y+  2z =  5

Now subtract this new equation from equation 3:

-2x + 4y - 2z = 10  (Eq 3)

 5x -   y+  2z =  5   [

 3x +3y = 15   [Equation A]

=================

Use equations 1 and 2 to eliminate z:

   2x +  y +3z = 12   (Eq. 1)

      x - 2y +  z = -5   (Eq. 2)

   2x +  y +3z = 12

(-3)(x - 2y +  z = -5)  [Multiply Eq. 2 by (-3)]

    -3x + 6y -3z = 15

Now add the resulting two equations.

   2x +   y + 3z = 12     (Eq. 1)

  -3x + 6y -3z =  15       (Eq,2 times -3)

   -x   +7y         = 27    [Equation B]

=============

  Eliminate x with the 2 resulting equations (from above)

  3x +3y = 15  [Equation A]

   -x +7y = 27  [Equation B]

----

   3x +3y = 15

   3*(-x +7y = 27)  [Multiply the Equation B by 3]

  -3x +21y = 81     [Aha - this equation has a -3x term, exactly what we need to eliminate the x term in Equation A]

---

Now add the two resulting equations:

    3x +3y = 15

   -3x +21y = 81

            24y = 96  [The x term disappears.  But we'll "find x" later]

                 y = 4   [Divide both sides by 24]

Find y and z:

Since y = 4,

-x  +7y   = 27 (From above, Equation B]

-x = -7y + 27

 x = 7y - 27

x = 7(4)-27

 x = 1                  [Looking good]

=====

Find z:  (Use y = 4 and x = 1)

x - 2y + z = -5  [Equation 2]

(1) -2*(4) + z = -5

1 - 8 + z = -5

z = 2

Check:

Do the original equations work when x = 1, y = 4, and z = 2?

Results:  

1.    2x + y +3z = 12      

     (1) + (4) +3(2)    YES, this equals 12

2.     x - 2y + z = -5  

       (1)  -2*(4) + (2)   YES, this equals -5

3.    5x - y+ 2z = 5

       5(1) - (4) + 2(2)   YES, this equals 5

x = 1, y=4, and z=2

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