anonymous
  • anonymous
Whats the formula I use to solve questions like this? 4x + y = 13 x + 4y = -8
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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jamiebookeater
  • jamiebookeater
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OakTree
  • OakTree
There's isn't a formula, per se. But there is a method that works every time. Do you want me to help you go through it?
anonymous
  • anonymous
definitely
uri
  • uri
@metalgearraiden Elimination?

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OakTree
  • OakTree
Okay. So there are two different methods. One of them, as said above, is elimination, and the other is substitution. For this one, substitution is probably best, as we already have a variable that doesn't have a coefficient in front of it. Good so far?
anonymous
  • anonymous
i see, so i need to plug in the first part into the second?
OakTree
  • OakTree
Right. So we take the first and rewrite it as an equation of the form y=____________. Can you do that?
anonymous
  • anonymous
thats the part that im confused on, what to plug in. its going to be y = 4 - 13?
OakTree
  • OakTree
Not quite. To get the y alone, we're going to have to subtract 4x from both sides, right? So if we subtract 4x from both sides, what does it look like?
anonymous
  • anonymous
y = 4x(- 4) = -8 (-4)
anonymous
  • anonymous
? oops 4y*
OakTree
  • OakTree
No, not quite. All I'm looking for is y=13-4x. See? We subtract 4x from both sides. Understand?
anonymous
  • anonymous
oh, so you just move the four over
anonymous
  • anonymous
with the x
OakTree
  • OakTree
Right. So now we plug that into the second equation and we get\[x + 4(13-4x) = -8\]You see where that came from?
anonymous
  • anonymous
y=13-4x x4(13-4)=-8 just replace y. i see
OakTree
  • OakTree
Great. So now simplify. Simplify that equation down as much as you can. What do you get? You should get something like x = ________.
jdoe0001
  • jdoe0001
http://www.youtube.com/watch?v=KL5mZ1gArQE
OakTree
  • OakTree
@jdoe0001, people are on this forum for live help, not just the way to finish the problem.
anonymous
  • anonymous
x = 36 = -8. im a little stumped on the reduction part also.
OakTree
  • OakTree
Okay, I'll help you. Start by distributing the 4 to the terms in the parenthesis. Do you know what that means?
anonymous
  • anonymous
multiply 4 by both of them?
OakTree
  • OakTree
Right. So what does that give you?
anonymous
  • anonymous
52 and 16
OakTree
  • OakTree
Write out the expression with plus, minus, and variables.
anonymous
  • anonymous
x = 4 (13*4 - 4*4) = -8
OakTree
  • OakTree
I was thinking more like\[x + 52 - 16x = -8\]So\[-15x = -60\]So\[x=4\]See?
anonymous
  • anonymous
oh i took a step back. so after solving inside the parenthesis i can advance. how did you get the 15 out of that exactly?
OakTree
  • OakTree
It's \[x-16x = -15x\]Combining like terms. OK?
anonymous
  • anonymous
gotcha
anonymous
  • anonymous
is y=3 then?
OakTree
  • OakTree
Great. So from here on out it's easy - we have an x, so we plug it in somewhere to get a y.\[4(4) + y = 13\]So\[16 + y =13\]So \[y=-3\]So our solution is \[(4,-3)\]And we're done. Good?
anonymous
  • anonymous
i think i get it now
OakTree
  • OakTree
Great. Glad to help.
anonymous
  • anonymous
its appreciated
wolf1728
  • wolf1728
Since you asked for a formula, there is something called Cramer's rule in which you set up determinants and evaluate them. I think it is just as complex as the usual method. Still, do an iteret search for it.

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