## MeganDarling 3 years ago Really need help! Been trying to solve for a while. 1. Solve the system by using a table. 3y=4x+7 , -4x-4y=28. These are the possible solutions:(–4, –3),(–3, –4), (4, 3),(3, 4). 2.Solve by graphing. -3x-y=-10, 4x-4y=8. possible solutions:(-1,3), (3-1), (1,3), (3,1)

1. MeganDarling

Also help with this problem : The spreadsheet shows the monthly revenue and expenses for a new business. Use the models to predict the month in which revenue will equal expenses. Possible answers: October September August May

2. MeganDarling

help with any of them would be really appreciated (:

3. L.T.

4. MeganDarling

your estimate is as good as any haha. I have no clue so even an educated guess is better than nothing

5. MeganDarling

I honestly just suck horribly at solving systems of any sort x.x

6. L.T.

I answered it that way by reproducing the pattern of increase in the revenue and expense columns--that is, by adding differences in a row. Does that sound legitimate?

7. MeganDarling

Sounds alright to me haha

8. L.T.

I think I can solve the system, but I'm not sure what is meant by table. Is it all right if you use substitution and elimination?

9. MeganDarling

I would just really like some help with the 1st two because there are lot's of other questions like them, including on upcoming tests. That I really don't want to get wrong :/

10. MeganDarling

Yeah that's what I was trying to do. I however looked up solving solutions on google and it showed a way to do it where you used a graph to figure out where the two lines crossed. It didn't make sense with my equation though.

11. satellite73

$-3x-y=-10$$4x-4y=8$ first equation is the same as $$y=-3x+10$$ so you can replace $$y$$ in the second equation by $$-3x+10$$ with judicious use of parentheses you get $4x-4(-3x+10)=8$ and now you have one equation and one variable to solve

12. satellite73

you get $4x+12x-40=8$ $16x-40=8$ $16x=48$ $x=48\div 16=3$

13. MeganDarling

As long as it end up with an x and a y and they are one of the options above I really don't understand why it matters so much how we got it haha. I suppose in some cases it really matters but.. Thanks satellite that makes sense. I'll try writing it out.

14. satellite73

hope the steps are claere

15. MeganDarling

yeah I think so, so what next?

16. satellite73

now that you have $$x=3$$ you can replace $$x$$ by 3 in either equation to solve for $$y$$

17. satellite73

for example we know $$y=-3x+10$$ and we know $$x=3$$ making $$y=-3\times 3+10=-9+10=1$$

18. MeganDarling

okay haha, I think I get that too x.x

19. satellite73

solving by graphing is too much work, and besides, if the answer is $$(-\frac{1}{7}, \frac{5}{7})$$ for example you will never know it from the graph

20. MeganDarling

I know I really hate it too :/ Then again I hate all math. But it's what they are making us do so .

21. satellite73

yes, sometimes math (especially this kind) is hateful that is why they invented computers for example, here is the answer to the first one http://www.wolframalpha.com/input/?i=+3y%3D4x%2B7+%2C+-4x-4y%3D28

22. MeganDarling

oh wow that's really cool! Thanks alot.