0
$\begingroup$

The solution to the system $4y=3x+7$ and $9x+4y-139=0$ is shown below.

enter image description here

I solved for the solution and found that the answer is correct, and is $(11, 10)$. But, what is the mistake that is made here? I'm assuming the strategy is incorrect because it does not look like it would work with different situations involving systems.

$\endgroup$
  • 1
    $\begingroup$ It's correct and that's how they are solved, there are quicker method though $\endgroup$ – Oussama Boussif Aug 12 '15 at 18:25
  • $\begingroup$ So essentially she just simplified both equations, and then solved? $\endgroup$ – Madison Aug 12 '15 at 18:56
  • $\begingroup$ Yes, she just subsituted and rearranged to get the solution that's how it's done $\endgroup$ – Oussama Boussif Aug 12 '15 at 18:58
0
$\begingroup$

As Oussama mentioned, there is an easier way to look at this. Write the first equation as: $$3x-4y=-7,$$ and the second equation as: $$9x+4y=139.$$ Then, we have: \begin{align} 9x+4y &= 139\\ 3x-4y &= -7. \end{align} Add the two equations together to get: \begin{align} 9x+4y &= 139\\ 3x-4y &= -7\\ \hline \\ 12x&= 132. \end{align} Notice that this method didn't require as many algebraic manipulations. Now, solve for $y$ just as before and you are done.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.