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toneisha · Nov 17, 2011, 08:26 AM

math x=7y-42x-3y=14

Curlyben · Nov 17, 2011, 08:34 AM

Seems to have become a little jumbled.
Would you please clarify your question.

jcaron2 · Nov 17, 2011, 11:25 AM

Originally Posted by toneisha

math x=7y-42x-3y=14

I think that's supposed to be two different equations, yes?

x=7y-42 and
x-3y=14

If so, the first equation tells you exactly what x is equal to. You can just substitute that expression in place of the x in the second equation. In other words, wherever you see an x in the second equation, write (7y-42) instead.

That will give you an equation with only one variable, y, which you should be able to easily solve for. Then you just have to plug that y value back into the first equation to get the value of x.

If you want to check your answers when you're all done, plug the values you got for x and y into both equations, and make sure they work out to be true. (For the second equation, for example, after you plug in x and y, you should end up with 14 = 14).

Aurora2000 · Nov 18, 2011, 08:15 AM

I am a newbie, and I first apologize if mimeTex is not good.

If it reads $x=7y-42,\ x-3y=14$ , then see jcaron2's answer.
If it reads $x=7y-4,\ 2x-3y=14$ , you have 2 (equivalent) choices:

1. Substitute $7y-4$ in place of $x$ , thus you have $2(7y-4)-3y=14$
2. $x=7y-4$ is the same as $2x=14y-8$ , then the difference between these equations gives you $0=11y-22\Longrightarrow\ y=2$

In both cases you have a one variable equation. There is no need to check solutions if you do things correctly, and linear equations never gets problems (as sign choices, singularities, etc.).

jcaron2 · Nov 18, 2011, 11:22 AM

I bet your interpretation is correct (the one where the gap is between the 4 and the 2x, not the 42 and the x).