## Systems of equations: solve x - y = -5, x + 3y = 3 in 3 ways

Simplificatation, evaluation, linear equations, linear graphs, linear inequalities, basic word problems, etc.
mizkej
Posts: 4
Joined: Thu Apr 23, 2009 3:40 am
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### Systems of equations: solve x - y = -5, x + 3y = 3 in 3 ways

Hi everyone! Thanks for all of your help on the last question. I ended up with an A on my last test. Talking to you really helped and when I saw the questions on the test I knew what to do.

I am stuck again. The question says to use three methods to solve for the following system of equations.

x-y=-5
x+3y=3

I need to solve by graphing, the addition method and the substitution method.

I think I have solved by graphing, please let me know if I have done this part correctly

the points I came up with are (0,-5) (-5,0) and for the second one (0,1) (1,0)

the addition method is where I beging to really struggle... this is what I have written

x-y=-5
x+3y=3
_______
2x+2y=-2

as for the substitution method... which was easy in class.... I now.. dont have a clue

stapel_eliz
Posts: 1628
Joined: Mon Dec 08, 2008 4:22 pm
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...use three methods to solve for the following system of equations.

x-y=-5
x+3y=3

I need to solve by graphing, the addition method and the substitution method.
To solve by graphing, draw the two lines and look for where they cross.

To learn how to solve by addition and elimination, try here and here.

For instance:

. . . . .x + 3y = 3

. . . . .x = -3y + 3

Substituting:

. . . . .(-3y + 3) - y = -5

. . . . .-3y - y + 3 = -5

. . . . .-4y = -8

...and so forth. On the other hand:
1x - 1y = -5
1x + 3y =  3

-1x + 1y = 5
1x + 3y = 3
------------
4y = 8
...and so forth, by "elimination" of the x-variable.