Posted by **please help!!!** on Tuesday, January 18, 2011 at 10:53pm.

i dont get these please help me:

use the subtitution method to solve the linear system

1)3x+y=0 x-y=4

2)y=-3x-1 x-3y=3

3)3x-y=9 2x+y=6

4)x-2y=0 3x+y=0

Thank you!!:)

- math(algebra 1) -
**helper**, Tuesday, January 18, 2011 at 11:17pm
1)3x + y = 0, x - y = 4

Pick and equation, and solve for either x or y

x - y = 4

x = 4 + y

Substitute, x = 4 + y, for x, in the other equation and solve for y

x = 4 + y

3x + y = 0

3(4 + y) + y = 0

12 + 3y + y = 0

12 + 4y = 0

4y = -12

y = -3

substitute y = -3 in either equation to find x

x - y = 4

x - (-3) = 4

x + 3 = 4

x = 1

Now you try the others

- math(algebra 1) -
**please help!!**, Tuesday, January 18, 2011 at 11:47pm
so are these correct?

2)y=-3x-1 x-3y=3

x=0 y=-1???

3)3x-y=9 2x+y=6

dont know help??

4)x-2y=0 3x+y=0

please help!!! i dont know how you changed x - y = 4 to x = 4 + y tell me please

Thanks!!

- math(algebra 1) -
**helper**, Wednesday, January 19, 2011 at 12:57pm
2) you are correct

x - y = 4

add + y to both sides

x - y + y = 4 + y

x = 4 + y

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