Solve for x in the system 3x + 4y = 8, y = 3x + 17

Makita

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Nov 16, 2006
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Okay, question two, (I'm glad I heard about this site, now I can actually understand what I'm learning!) Solve for x any in the system:

3x + 4y = 8
y = 3x + 17

So solve first for x:

3x + 4y = 8
3x = 8 - 4y

(this is where my question lies, when I divide 3 from the left side do you divide it using the 8 or the -4y?

The next step would be to substitute x=(what I came up with) in the second equation.
 
Why not just do this. Given
3x+4y=8
y=3x+17

then 3x+4(3x+17)=8.
Solve that.
 
Okay so 3x+4(3x+17)=8.
3x+12x+68=8
15x=-60
x=-4

3x+4y=8
3(-4)+4Y=8
-12+4y=8
4y=20
y=5

(-4, 5)

THANKS FOR YOUR HELP AGAIN :D
 
Re: Solve for x in the system

Makita said:
3x+4y=8 [1]
y=3x+17 [2]
Easier still:
3x + 4y = 8 [1]
-3x + y = 17 [2] ; add them together:
5y = 25
y = 5
 
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