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Mathematics 42 Online
OpenStudy (anonymous):

solve 3x-4y=-4 over x+2y=-8

OpenStudy (anonymous):

I don't understand what's being asked.

OpenStudy (anonymous):

3x-4y=-4 x+2y=-8

OpenStudy (anonymous):

there's not enough information being shown

OpenStudy (shadowfiend):

That is enough information. I assume you're trying to solve for x and y.

OpenStudy (anonymous):

i agree ^^

OpenStudy (shadowfiend):

So the first step in these situations is ideally to try to get one of the variables in terms of the other. In this case, we'll try to get $$x$$ in terms of $$y$$. We'll pick the second equation because it's slightly easier: \begin{align} x + 2y &= -8\\ x &= -8 - 2y \end{align} So far, so good. We can now plug in for $$x$$ in the first equation: $3(-8 - 2y) - 4y = -4$ Now we can solve for $$y$$: \begin{align} -24 - 6y - 4y &= -4\\ -24 - 10y &= -4\\ -10y &= -4 + 24 = 20\\ y &= \frac{20}{-10} = -2 \end{align} So we now know that $$y = -2$$. We can plug $$y$$ back into our equation for $$x$$ and get $$x$$: $x = -8 - 2y = -8 - 2(-2) = -8 + 4 = -4$ Now we have that $$y = -2$$ and $$x = -4$$, but, we should plug back into both of the original equations to make sure that our result matches the equations: $3x - 4y = 3(-4) - 4(-2) = -12 + 8 = -4$ That one matches. $x + 2y = -4 + 2(-2) = -4 - 4 = -8$ And so does that one. The solution is right! Hope that helps.

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