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Home Q & A Board Science-Related Homework Help Mathematics
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dav1444 dav1444
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11 years ago
x+y=4
2x+3y=-7
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wrote...
#1
11 years ago
I will be using substitution to solve this problem.
First, you find a way to get rid of one of the variables.
I multiplied the top equation by negative 2 ->  -2(x+y=4) ->(-2x-2y= -8) Then, I added the two equations together (-2x-2y= -8)+ (2x+3y= -7)     and I got y= -15     The, I substituted y for -15 in the first equation and solved it: x+y=4    x-15=4     x=19
x=19, y=-15
The final step is to check the answers
2(19) + 3(-15)= -7    38 - 45= -7     -7=-7
wrote...
#2
11 years ago
You want to get eithe x or y alone.  Multiply the top equation by -2.
-2 (x+y = 4) = -2x - 2y = -8   Next add the 2 equations together.

-2x - 2y = -8
2x + 3y = -7
------------------
       y = - 15
Plug this value into either equation to solve for x.

x -15 = 4   Add 15 to both sides of the equation to get x
x = 4 + 15 = 19
For a check you can plug the values of x & y into equation & the
equation should work.
Example: x + y = 4
19 + (-15) = 4
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