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Question 638214: Solving System of Linear Equations by Elimination. My math this week shows an example and I do not understand where the answer comes from. I will provide the example and show where I got lost.
2a + 3b = 25
-2a + b = 11
I understand this section
2a + 3b = 25
-2a + b = 11
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4b = 36
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4 4 = b=9
2a + 3(9)= 25 <----- this is where my confusion is: the answer it shows it as -1 BUT HOW DID IT GET THIS ANSWER?
I get the fact that it is a point, I see that the answer is (-1,9) but I do not know how to get the -1, I do know where the 9 came from but not the -1.
I hope this is example enough for help. I have similar questions that I have due but I cannot find out the correct answer if I am missing this one step.
I did one with out the example and came to the same problem of finding one point but not the other. I got it wrong because of that one missing part. I will also show what I did.
6a + 5b = 17
-6a + b = 25
6a + 5b = 17
-6a + b = 25
_____________
6b = 42
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6 6 which is b = 7
6a + 5(7)=17.....AGAIN I AM STUCK! the correct answer was -3 but I do not see how?
Also is there a easier way of doing this math?
Found 2 solutions by reviewermath, richwmiller:
Answer by reviewermath(1029)   (Show Source):
Answer by richwmiller(17219)  (Show Source):
You can put this solution on YOUR website! second system
b = 7
now get a which is -3
6,5,17
-6,1,25
divide row 1 by 6/1
1,5/6,17/6
-6,1,25
add down (6/1) *row 1 to row 2
1,5/6,17/6
0,6,42
divide row 2 by 6/1
1,5/6,17/6
0,1,7
We now have the value for the last variable.
We will work our way up and get the other solutions.
add up (-5/6) *row 2 to row 1
1,0,-3
0,1,7
final
1,0,-3
0,1,7
1,0,-3
0,1,7
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