Let , R. If the system of equations 3x + 5y + z = 3 7x + 11y - 9z = 2 97x + 155y - 189z = has infinitely many solutions, then + 2 is equal to :
- 24
- 25
- 27
- 22
Answer
(2) 25
Solution
For infinitely many solutions, eliminating x, y, z must leave an identity 0 = 0. First remove y:
Eq. (1) × 31 − Eq. (3): -4x + (31 + 189)z = 93 - …(i)
Eq. (2) × 155 − Eq. (3) × 11: 18x + 684z = 310 - 11 …(ii)
Now remove x by 9 × (i) + 2 × (ii):
(279 + 3069)z = 1457 - 31
This must hold for every z, so both sides vanish:
279 + 3069 = 0, so = -11
1457 - 31 = 0, so = 47
Hence + 2 = 47 - 22 = 25.
Answer: (2)