# system

• Apr 9th 2008, 08:46 AM
gdespina
system
I go to the first class of lyceum and I have to solve the systems in algebra:

x+y=-1
2x+2y=-2

and another one:

x+2y=13
3x+y=4

Thanks a lot.

Pigaino stin proti lukeiou kai prepei na luso ta sustimata stin algebra:

x+y=-1
2x+2y=-2

kai akomi ena:

x+2y=13
3x+y=4

Parakalo boithiste me sta mathimatika.

Euxaristo polu.
• Apr 9th 2008, 08:50 AM
Moo
Hello,

x+y=-1
2x+2y=-2

There is an infinity of solutions for this one as one is the double of the other...

x+2y=13
3x+y=4

from the first one, we can say that x=13-2y

thus 3(13-2y)+y=4
39-6y+y=4
-5y=-35
y=7

x=13-2*7=-1

(-1,7) is solution
• Apr 9th 2008, 09:07 AM
gdespina
Thanks.

And what about the other system?

x+y=-1
2x+2y=-2
• Apr 9th 2008, 09:13 AM
topsquark
Quote:

Originally Posted by gdespina
Thanks.

And what about the other system?

x+y=-1
2x+2y=-2

Quote:

Originally Posted by Moo
Hello,

x+y=-1
2x+2y=-2

There is an infinity of solutions for this one as one is the double of the other...

-Dan
• Apr 9th 2008, 09:14 AM
Moo
Quote:

There is an infinity of solutions for this one as one is the double of the other...
x=-1-y

And it works for any couple that verify it.

For example :

(1,-2)
(2,-3)

etc...
• Apr 10th 2008, 05:10 AM
gdespina
Yes..

x+y=-1
2x+2y=-2

the first -> x=-1-y

and the second:

-> 2(-1-y)+2y=-2
-2-2y+2y=-2
-2y+2y=-2+2
0=0

is this correct?

how could this system solve?
• Apr 10th 2008, 08:35 AM
masters
Same line
If you divide your second equation by 2, it turns out to be the same as the first equation....thus, the same line. If two lines coincide with each other (one on top of the other), then there are an infinite number of solutions.

Remember to check the slopes of the lines in a system. If the slopes are equal, but the y-intercepts are different, then there are no solutions. The lines are parallel.

Dale