jagr2713
  • jagr2713
x-3y=-9 6x+y=3
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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chestercat
  • chestercat
I got my questions answered at brainly.com in under 10 minutes. Go to brainly.com now for free help!
jagr2713
  • jagr2713
i dont understand this @freckles
steve816
  • steve816
How does a 99 rated mathlete not know how to do system of equations O.o
jagr2713
  • jagr2713
Well when you haven't done math in a while u forget things.....

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IrishBoy123
  • IrishBoy123
|dw:1442268783821:dw|
jagr2713
  • jagr2713
ok i know the part where u add them and stuff but i just need help in the beginning. How do u find what to multiply them with?
IrishBoy123
  • IrishBoy123
when they are set out like that, just imagine adding them and knocking out an x or a y so, let's do it again
IrishBoy123
  • IrishBoy123
|dw:1442269218613:dw|
jagr2713
  • jagr2713
wait why did u use 1 and 2
IrishBoy123
  • IrishBoy123
if you meant, the (1) and (2) in brackets to identify the equations, and just a habit is that what you were referring to?
jagr2713
  • jagr2713
Because my teacher taught me to multiply them by a number and then add then and cancel the x or y u used etc
IrishBoy123
  • IrishBoy123
loads of ways to do these eg |dw:1442269699628:dw|
IrishBoy123
  • IrishBoy123
can i ask , do you work on the OS website??
jagr2713
  • jagr2713
whats the easiest way? can u do in equation form cause the drawing is losing me
jagr2713
  • jagr2713
do i work on the website?
IrishBoy123
  • IrishBoy123
yes
jagr2713
  • jagr2713
what does that mean?
IrishBoy123
  • IrishBoy123
are you part of the OS team?
jagr2713
  • jagr2713
Oh yes...
IrishBoy123
  • IrishBoy123
easiest way is substitution, IMHO. as in, it's pure method. so, from the first equation, which is \(x - 3y = -9\), you can say \(x = 3y - 9\) then in the second, which is \(6x + y = 3\), you can say \(6(3y - 9) +y = 3\) so \(18y - 54 + y = 3\) or \(19y = 57\), \(y = 3\)
IrishBoy123
  • IrishBoy123
so you code this site?!
jagr2713
  • jagr2713
OOOHOHO you have to change the x-3y=*9 in x=3y-9 and lets stay relevant :D u can message me the other questions
IrishBoy123
  • IrishBoy123
OK!!
jagr2713
  • jagr2713
But what if its x+3y=-9 does 3y become positive cause u move it?
IrishBoy123
  • IrishBoy123
if x + 3y = -9 then x = -3y - 9
IrishBoy123
  • IrishBoy123
because x+3y-3y = -9-3y
jagr2713
  • jagr2713
so i got 6(3y-9)+y=3 18y-54+y=3 +y +y 19y-54=3 +54 +54 19y=57 y=3
jagr2713
  • jagr2713
so now u plug it into the x too get x right? x-3(3)=-9 x+9=-9 -9 -9 x=-18 so we got (-18,3)
jagr2713
  • jagr2713
??
IrishBoy123
  • IrishBoy123
if you know that y = 3, plug that into one of the original equations to find x
IrishBoy123
  • IrishBoy123
eg, if x - 3y = -9 what is x if y = 3
IrishBoy123
  • IrishBoy123
or if 6x + y = 3 what is x if y = 3??
jagr2713
  • jagr2713
you plug it into the x-3y=-9 right?
IrishBoy123
  • IrishBoy123
into either, you want to know when they meet
jagr2713
  • jagr2713
it says -18,3 is wrong
jagr2713
  • jagr2713
wait don't i need another point?
IrishBoy123
  • IrishBoy123
i thought we had agreed 0, 3 ?!?!
IrishBoy123
  • IrishBoy123
as in x = 0
IrishBoy123
  • IrishBoy123
and y = 3
jagr2713
  • jagr2713
OOHOHOHO i did it wrong ok so i need another set of points to connect it.
IrishBoy123
  • IrishBoy123
indeed you might! gtg
jagr2713
  • jagr2713
So how do i get it?
jagr2713
  • jagr2713
@freckles
IrishBoy123
  • IrishBoy123
really sorry @jagr2713 i gotta go sleep i am in europe, i guess you are somewhere else my condolensces!!!!
jagr2713
  • jagr2713
Its ok
jdoe0001
  • jdoe0001
are you meant to solve by either substitution or elimination?
jagr2713
  • jagr2713
Graphing them
jagr2713
  • jagr2713
i got the answer 0,3 just need another point
jdoe0001
  • jdoe0001
well... where the graph of two equations meet, is where the answer is :) hm if 0,3 is the answer.... isn't that what you needed? :)
jagr2713
  • jagr2713
Yea but thats only one point need 2 for a line
jdoe0001
  • jdoe0001
hmmm one sec
jagr2713
  • jagr2713
ok :D
jagr2713
  • jagr2713
here use this i did another question x-3y=-3 3x+y=1 i got (0,1)
jdoe0001
  • jdoe0001
..is that another one?
jagr2713
  • jagr2713
Yea i just change questions i got 0,1 but need another point
jdoe0001
  • jdoe0001
hmmm thought you were supposed to just graph them?
jagr2713
  • jagr2713
Yea it say solve the following system of equation by graphing them
jdoe0001
  • jdoe0001
well... I'd just graph them then :) lemme do a quick table
jagr2713
  • jagr2713
ok thanks
jagr2713
  • jagr2713
wait do we just do the x|y thing and put 0 for x and ory?
jagr2713
  • jagr2713
|dw:1442273690049:dw| like that?
jdoe0001
  • jdoe0001
yeap to make a line, all you need is 2 points so just pick two random "x" to get two "y"s
jagr2713
  • jagr2713
OHH so |dw:1442273743049:dw|
jagr2713
  • jagr2713
other is 0,3 2,0
jdoe0001
  • jdoe0001
hmm yes \(\begin{array}{llll} x-3y=-3\implies &\cfrac{x+3}{3}={\color{brown}{ y}} \\ \quad \\ 3x+y=1\implies &{\color{brown}{ y}}=1-3x \end{array} \\ \quad \\ \qquad \qquad \begin{array}{ccllll} x&y \\\hline\\ &\frac{x+3}{3}\\ \\\hline\\ &\frac{x+3}{3}\\ 0&1\\ -3&0 \end{array}\qquad \begin{array}{ccllll} x&y \\\hline\\ &1-3x \\\hline\\ 0&1\\ 4&-11 \end{array}\)
jagr2713
  • jagr2713
where did u get they -3 from?
jdoe0001
  • jdoe0001
x-3y=-3 <--- 3x+y=1
jagr2713
  • jagr2713
is this correct (0,3) (-9,0) and (0,3) (2,0) ?
jdoe0001
  • jdoe0001
hmmm 0, 3 is not, -9,0 isn't either
jdoe0001
  • jdoe0001
x =0 x -3y=-3 0-3y=-3 y = (-3)/(-3) y =1
jagr2713
  • jagr2713
x-3y=-9 -3y=-9 y=1/3 x-3y=-9 x=-9
jdoe0001
  • jdoe0001
x=-9 (-9)-3y=-3 -3y=-3+9 -3y=+6 y=(6)/(-3) y=-2
jagr2713
  • jagr2713
wait this is confusing me dont u put 0 for them?
jdoe0001
  • jdoe0001
wel... you said it was x-3y=-3 3x+y=1 but now you seem to have changed it some
jagr2713
  • jagr2713
OHOHOHO I've been doing the wrong problem... :D KML
jagr2713
  • jagr2713
I WAS LOOKING AT THE QUESTION LOL
jagr2713
  • jagr2713
i got (0,1) (-3,0) and (0,1) (3,0)
jdoe0001
  • jdoe0001
but all you need to graph a line is two points \(\begin{array}{llll} x-3y=-3\implies \cfrac{x+9}{3}={\color{brown}{ y}}\\ 6x+y=3\implies {\color{brown}{ y}}=3-6x \end{array}\) http://fooplot.com/#W3sidHlwZSI6MCwiZXEiOiIoeCs5KS8zIiwiY29sb3IiOiIjM0IxRENGIn0seyJ0eXBlIjowLCJlcSI6IjMtNngiLCJjb2xvciI6IiNENDExMTEifSx7InR5cGUiOjEwMDAsIndpbmRvdyI6WyItNi41NCIsIjYuNDYiLCItMi40OCIsIjUuNTIiXX1d
jagr2713
  • jagr2713
D: it says my answer is wrong... i did the x|y thing
jdoe0001
  • jdoe0001
check yours PEMDAS I'd think
freckles
  • freckles
I'm confused... Are you saying you got 3 different solutions for x-3y=-3 3x+y=1 ? You should only get one solution, infinitely many solutions, or no solutions for system of linear equations.
jagr2713
  • jagr2713
OHH my friend told me to use y=mx+b
freckles
  • freckles
why? aren't you trying to solve the system x-3y=-3 3x+y=1 ? or is that not the question?
jagr2713
  • jagr2713
yes by graphing it thou but i did it and getting it wrong D:
freckles
  • freckles
you should just get a point for the solution of this system: you will see that when graphing these two lines that they will share a common point that point is the solution x-3y=-3 -3y=-x-3 y=1/3*x+1 --- 3x+y=1 y=-3x+1 so graphing both y=1/3*x+1 and -3x+1 we have something that looks like this: |dw:1442275696567:dw| the solution is given at the point where both lines touch each other (cross each other; intersect each other)
freckles
  • freckles
|dw:1442275792808:dw| so this point I darkened is the solution because is the point that two lines have in common
jagr2713
  • jagr2713
wait can u try thing one x-2y=-2 4x+y=1
freckles
  • freckles
were you trying to write in y=mx+b form to graph the lines to find the point ?
jagr2713
  • jagr2713
yea i was using that
freckles
  • freckles
ok well try writing x-2y=-2 in that form
jagr2713
  • jagr2713
2y=x+2 right?
freckles
  • freckles
so you subtracted x on both sides and multiplied -1 on both sides? x-2y=-2 subtracted x on both sides -2y=-x-2 multiplied both sides by -1 2y=x+2 this is correct so far then just divide both sides by 2
jagr2713
  • jagr2713
yea i got y=1/2x+1
jagr2713
  • jagr2713
then u graph it by going to (0,1) then rise over run
freckles
  • freckles
that sounds great so y=1/2x+1 says the y-intercept is 1 and the slope is 1/2 |dw:1442276083294:dw| right so you get something like this now we also need to graph 4x+y=1 on that same graph
freckles
  • freckles
4x+y=1 is equivalent to y=-4x+1 can you try graph that we should actually already see the solution even before graphing
jagr2713
  • jagr2713
yea we got 0,1 then rise over run -4/1
freckles
  • freckles
so before graphing you should see that (0,1) is a point on both graphs where both graphs differ in slope therefore (0,1) is the solution
jagr2713
  • jagr2713
yea 0,1 is the slope so we go down 4 and move 1 to the left right?
freckles
  • freckles
(0,1) is the y-intercept the slope is -4/1 so we move down from the y-intercept 4 units and to the right once
jagr2713
  • jagr2713
Oh right 1 sorry my friend told me left....
jagr2713
  • jagr2713
OMG your the best :D
jagr2713
  • jagr2713
can u help with one more but this one is substitution
freckles
  • freckles
sure
freckles
  • freckles
one more then I have to roll my croissant dough
jagr2713
  • jagr2713
ok :D 4x+y=24 y=2x
freckles
  • freckles
replace first y with (2x) solve 4x+2x=24 for x
jagr2713
  • jagr2713
don't you reverse it like y=4x+24 and plug into x y=2(4x+24)
freckles
  • freckles
the second equation says y=2x so you insert that y here: 4x+y=24 to get 4x+2x=24 anyways you can't replace x with 4x+24 because we aren't given x=4x+24 unless you already know that x=-8 which x doesn't -8 and also 4x+y=24 is not equivalent to y=4x+24
jagr2713
  • jagr2713
wait how did u get 4x+2x=24
freckles
  • freckles
\[\color{red}{y=2x} \\ 4x+\color{red}{y}=24 \\ \\ 4x+\color{red}{2x}=24\]
freckles
  • freckles
I replaced y with 2x because one of the equations said y=2x
jagr2713
  • jagr2713
Wait i understand igtg thanks for the help
freckles
  • freckles
k peace

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