I'm really not understanding how to solve this problem and this will be on my final.

What is the solution of the system?
4x - 4y = -40
-4x + 7y = 55

Question

I'm really not understanding how to solve this problem and this will be on my final. 

What is the solution of the system?
4x - 4y = -40
-4x + 7y = 55

hero · Answer

Hint: Add them together

hero · Answer

(4x - 4x) + (7y - 4y) = 55 - 40

hero · Answer

You can only add the equations together in cases where one of the variables will cancel. This is one of those cases.

anonymous · Answer

So I would get (5,5)

anonymous · Answer

y = x+10

I think.

anonymous · Answer

http://puu.sh/1zSbn

hero · Answer

@assaulth3ro911  

no bro

hero · Answer

@AstralDnB

They're not both positive. One coordinate is positive. The other, negative.

hero · Answer

You have to pay attention to signs.

anonymous · Answer

ok. I re-did everything and got (5,-5)

hero · Answer

Now you have it backwards

anonymous · Answer

Oh sorry about. Got excited and posted the answer backwards. Thnx for you help.