Linear equations in the form ax+by=c

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PinkOneAmong
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Could someone explain how I write an equation in the form ax+by=c?
Yesterday someone helped me learn how to write it in y=mx+b, but I'm not sure how to write it this way.
I have the co-ordinates of (1,-1) and (4,7)
How do I do this?
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mqb2766
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(Original post by PinkOneAmong)
Cou
ld someone explain how I write an equation in the form ax+by=c?
Yesterday someone helped me learn how to write it in y=mx+b, but I'm not sure how to write it this way.
I have the co-ordinates of (1,-1) and (4,7)
How do I do this?
Can you write that as y=mx+b. Post your answer.
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PinkOneAmong
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(Original post by mqb2766)
Can you write that as y=mx+b. Post your answer.
(1,-1) (4,7)
y=8/3x+-11/3 ?
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Ee13
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(Original post by PinkOneAmong)
(1,-1) (4,7)
y=8/3x+-11/3 ?
Multiply the y by the 3 then your left 3y=8x-11
Then move the 8x onto the other side so it would be 3y-8x=-11
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mqb2766
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(Original post by PinkOneAmong)
(1,-1) (4,7)
y=8/3x+-11/3 ?
y = 8/3x - 11/3
Looks good, check by subbing the two points in and make sure the equation balances.
You want the x term on the same side as the y term, so take 8/3x to the other side and post that.
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PinkOneAmong
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(Original post by mqb2766)
y = 8/3x - 11/3
Looks good, check by subbing the two points in and make sure the equation balances.
You want the x term on the same side as the y term, so take 8/3x to the other side and post that.
-8x+3y=-11?
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PinkOneAmong
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(Original post by Ee13)
Multiply the y by the 3 then your left 3y=8x-11
Then move the 8x onto the other side so it would be 3y-8x=-11
wouldn't that be in the wrong order?
ax+by=c?
so, wouldn't it be -8x+3y=-11 ?
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mqb2766
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(Original post by PinkOneAmong)
wouldn't that be in the wrong order?
ax+by=c?
so, wouldn't it be -8x+3y=-11 ?
Either is fine. Just understand how you did it.
It is more normal to do
8x - 3y = 11
Last edited by mqb2766; 1 month ago
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PinkOneAmong
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(Original post by mqb2766)
Either is fine. Just understand how you did it.
It is more normal to do
8x - 3y = 11
Ohhh, okay thankyou for your help, that was much easier than I had expected
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DFranklin
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(Original post by PinkOneAmong)
Ohhh, okay thankyou for your help, that was much easier than I had expected
Couple fo things to make sure you know:

You can multiply an equation of form ax+by = c by a (non-zero) constant and it still means the same thing.

If you already know y = mx + c, you can trivially rearrange this to get mx - y = -c, which is of the form you're asking for.
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