Die Einsetzungmethode
x + 2y- z = 2
1.) x = 2 - 2y + z
2x + y + 2z = 0
x + y + az = 1
1.) einsetzen
2 * ( 2 - 2y + z )+ y + 2z = 0
( 2 - 2y + z ) + y + az = 1
4 - 4y + 2z + y + 2z = 0
2 - 2y + z + y + az = 1
-3y + 4z = -4
-y + z * ( 1 + a ) = -1 | * 3
-3y + 4z = -4
-3y + 3z * ( 1 + a ) = -3
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4z - 3z * ( 1 + a ) = -1
4z - z * ( 3 + 3a ) = -1
z * ( 4 - 3 - 3a ) = -1
z = -1 / ( 1 - 3a )
z = 1 / ( 3a - 1 )
dann einsetzen in z.B.
-3y + 4z = -4
y = ...