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Heres the question, we're suppose to be using the method of addition and substitution

solve: x+y+z=4
2x-z=1
2y+z=1

I already eliminated X and Y, so I have it down to
-2y-3z=-7
-2x-z=7

Anybody know where to go from here? Thank you!

2007-10-11 05:57:55 · 5 answers · asked by sleepinbeauty52 2 in Education & Reference Homework Help

5 answers

2y - z = 1 => 2y = 1 + z => y = (1+ z) / 2
2x + z = 1 => 2x = 1 - z => x = (1 - z) / 2

(1+ z) / 2 + (1 - z) / 2 + z = 4
( 1 +z +1- z ) /2 + z = 4
2/2 + z = 4 => z = 4 -1 = 3
y = 4/2 =2
x = -2 /2 = -1

2007-10-11 06:05:56 · answer #1 · answered by Naoko 3 · 0 0

Not sure how you got the -2y-3z=-7 and the -2x-z=7.

z is common to both equations.

taking the first equation x+y+z=4
z=4-x-y

substitute 4-x-y for z in next two equations

2x-(4-x-y)=1
2x-4+x+y=1 then combine
3x-4+y=1 then add 4 to both sides
3x+y=5 therefore
y=5-3x

Next sub in z value in next equation 2y+z=1
2y+(4-x-y)=1 we get 2y+4-x-y=1
combining we get y+4-x=1, subtract 4 from both sides
y-x=-3

Next sub in y value we found in first equation y=5-3x
(5-3x)-x=-3 we get 5-3x-x=-3. Combine
-4x=-8 therefore
x=2

sub in x value in previous equation y-x=-3
y-(2)=-3 we get
y-2=-3 or y=-1

2007-10-11 13:35:35 · answer #2 · answered by the mazda mechanic 4 · 0 0

-2y-3z=-7
-2x-z=7

first of all lets use the sub method.

-z=2x+7

u gotta make the z positve so the next thing u gotta do is:

z= -2x-7

from there u substitute to the other equation

-2y-3(-2x-7)=-7

i hope that this helps... if anything just write back to me...:)

2007-10-11 13:12:13 · answer #3 · answered by Anonymous · 0 0

when u r solving 3 eqations u should not approach in this way.
the correct approach is
x+y+z=4........[1]
2x-z=1...........[2]
2y+z=1...........[3]


by adding [2] & [3] we get

2(x+y)=2 ..........x+y=1........[4]
by substituting [4] in [1] we get
z=3...........[5]


by using [5] & [2] we get
x=2.
and by [5] & [3] we get
y=-1

2007-10-11 13:09:43 · answer #4 · answered by vinod s 2 · 0 0

x+y+z=4
(z+1)/2+(1-z)/2+z=4
z+1+1-z+2z=8
z=3

2x-z=1
2x-3=1
x=2

2y+z=1
2y+3=1
y=-1

2007-10-11 13:05:19 · answer #5 · answered by Anonymous · 1 0

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