SOLUTION: 5a-b=12 7a-3b=20 find a and b.

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Question 699550: 5a-b=12
7a-3b=20
find a and b.
Answer by Stitch(470) About Me  (Show Source):
You can put this solution on YOUR website!
Given: 5A+-+B+=+12 and 7A+-+3B+=+20
Set both equations equal to zero
5A+-+B+-+12+=+0
7A+-+3B+-+20+=+0
Notice that you can make both equations contain -3B if you multiply the first equation by 3.
3%2A%285A+-+B+-+12%29+=+3%2A0
Simplify
15A+-+3B+-+36+=+0
Now both equations have a -3B in them.
Since both equations are equal to zero, you can set them equal to each other.
15A+-+3B+-+36+=+7A+-+3B+-+20
Add 3B to both sides
15A+-+36+=+7A+-+20
Subtract 7A from both sides
8A+-+36+=+-20
Add 36 to both sides
8A+=+16
Divide both sides by 8
highlight%28A+=+2%29
Now plug 2 into on of the given equations for A. Then solve for B
5A+-+B+=+12
5%2A%282%29+-+B+=+12
10+-+B+=+12
Subtract 10 from btoh sides
-B+=+2
Divide both sides by -1
highlight_green%28B+=+-2%29