What is the value of the x variable in the solution to the following system of equations?
7x - 2y = 21
4x + y = 57

- anonymous

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- schrodinger

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- anonymous

ummm is this algebra 2?

- anonymous

algebra 1, 2nd year taking it again

- anonymous

once i find the y , i put it in the the first equation right?

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- anonymous

I think so... i asked somebody if they could come and help since I need to understand this better as well since i sort of forgot haha :)

- anonymous

sorry hold on lemme see if that person will come... ;/

- anonymous

okay thank you (:

- anonymous

Hi @jim_thompson5910 thanks for coming :) I also do not understand this 100% haha :) u got my message then i take it? :)

- jim_thompson5910

double everything in the second equation to get
8x + 2y = 114

- anonymous

sorry (email)

- anonymous

and hi @apoorvk thanks for coming also!!! i appreciate it :)

- apoorvk

ohkay, @iheartfood - go on and post what you would have done in this problem, and don't worry if it's right or wrong.. :)

- jim_thompson5910

Now add the two equations
7x - 2y = 21
8x + 2y = 114
--------------
15x + 0y = 135
Now solve 15x = 135 for x

- anonymous

well i know you're supposed to solve for one, but i did not know you could do that (what @jim_thompson5910 wrote.... so that is another way you can do it??

- anonymous

is that how you do it?? simplify it into one larger equation??

- jim_thompson5910

that's one way to do it, there is more than one way

- anonymous

okay, what's another way to do it?? i think i remember that you can solve one equation and then plug it in but i couldn't do it for this one... ;/

- jim_thompson5910

you isolate one variable in terms of the other
then you substitute
4x + y = 57
y = 57 - 4x
------------------
7x - 2y = 21
7x - 2(57-4x) = 21
Now solve for x

- anonymous

x = 9 for my problem right? (:

- anonymous

oh okay cool :) soooo x=45??

- jim_thompson5910

you are correct, the answer to the first piece is x = 9

- anonymous

oops my bad nvm lol

- jim_thompson5910

hmm how did you get x = 45?

- jim_thompson5910

now that you know that x = 9, use this to find y

- anonymous

sorry by bad... lol it's 9 sorry!!

- anonymous

sooo you plug it in right??

- anonymous

so y=21 ???? and x=9 ???

- jim_thompson5910

yes, pick any equation dealing with y and plug in x = 9
7x - 2y = 21
7(9) - 2y = 21
Solve for y

- jim_thompson5910

and yes, y = 21

- anonymous

oh i used the second equation.. haha but it works both ways :) u get the same answer for both right?

- jim_thompson5910

oh the question was just "What is the value of the x variable in the solution to the following system of equations?"
so they just want x
Usually, they'll want both x and y

- jim_thompson5910

yes either equation works

- anonymous

oh okay cool! thanks!! i totally understand it now... :) what a refresher!! And @sommersquid did that help??? And thanks again for coming @jim_thompson5910 :)

- anonymous

yesss, it really did (: i just needed help with the second step but i got it now (: thank you so much everyone

- jim_thompson5910

yw

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