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If the system of equations ( -1)x+( -4)y+ z=5 x+( -1)y+( -4)z=7 ( +1)x+( +2)y-( +2)z=9 has infinitely many solutions, then 2+ is equal to
(4) 12
Infinitely many solutions =0.
R1 R1-R2, R2 R2-R3, R2 R2-R1 gives =-2( -3)(2 +1) =3 or - 12
=- 12: x 0, no solution (rejected)
=3: eq. (3) =2 eq. (2) - eq. (1) on both sides, so consistent
2+ =12
Answer: (4)
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