SOLUTION: 2x+y=-4 x+y=-7 Find the first variable and isolate it. Then solve for that variable. solve for the second variable find the numerical value of the first variable. (when I say

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Question 1190677: 2x+y=-4
x+y=-7
Find the first variable and isolate it. Then solve for that variable.
solve for the second variable
find the numerical value of the first variable.
(when I say the first variable it's any variable that you would want to start with...that's what my teacher said)
I don't really understand how to do this so could somebody please explain
Found 3 solutions by Alan3354, Theo, MathTherapy:
Answer by Alan3354(69443)   (Show Source): You can put this solution on YOUR website!
Same problem, different numbers.
-----------
2x+y=5
2y=2x-8 ---> y = x-4
Find the first variable (that you want to use) and isolate it then solve for it
---------
y is isolated and solved for in terms of x.
---
2x+y=5
Sub for y
2x + (x-4) = 5
3x - 4 = 5
3x = 9
x = 3
-----
y = x-4
y = -1
That's solved by substitution.
-----
Another way is elimination:
2x+y=5
2y=2x-8
----
2x +y = 5
2x-2y = 8
-------------- Subtract
3y = -3
y = -1
---
2x +y = 5
2x - 1 = 5
2x = 6
x = 3
Answer by Theo(13342)   (Show Source): You can put this solution on YOUR website!
your equations are:

2x + y = -4
x + y = -7

solve for x in the second equation to get:

x = -7 - y

replace x in the first equation with that to get:

2x + y = -4 becomes 2 * (-7 - y) + y = -4.

you have just changed one equation with two variable into one equation with one variable, allowing you to solve for that variable.

the equation to solve is:

2 * (-7 - y) + y = -4.
simplify to get:
-14 - 2y + y = -4
combine like terms to get:
-14 - y = -4
add 14 to both sides to get:
-y = -4 + 14
simplify to get:
-y = 10
multiply both sides by -1 to get:
y = -10

now that you solved for y, you can go back to your original equations to solve for x.
your original equations are:
2x + y = -4
x + y = -7

when y = -10 .....
2x + y = -4 becomes 2x -10 = -4 which becomes 2x = 6 which becomes x = 3.
x + y = -7 becomes x - 10 = -7 which becomes x = 3.
your solution is that y = -10 and x = 3.
both original equations are true with those values for x and y.

let me know if you have any questions or need further clarification.

here's a reference for you as well.
https://www.purplemath.com/modules/systlin4.htm
theo
Answer by MathTherapy(10552)   (Show Source): You can put this solution on YOUR website!
2x+y=-4
x+y=-7
Find the first variable and isolate it. Then solve for that variable.
solve for the second variable
find the numerical value of the first variable.
(when I say the first variable it's any variable that you would want to start with...that's what my teacher said)
I don't really understand how to do this so could somebody please explain 
That person's WRONG!!  

2x + y = - 4 ----- eq (i)

x + y = - 7____x = - 7 - y ---- eq (ii)

2(- 7 - y) + y = - 4 ----- Substituting - 7 - y for x in eq (i)

- 14 - 2y + y = - 4

- y = 10



x = - 7 - (- 10) ------- Substituting - 10 for y in eq (ii)

 

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