If the system of equations x + 4y - z = , 7x + 9y + z = -3, 5x + y + 2z = -1 has infinitely many solutions, then (2 + 3 ) is equal to :
- -2
- 2
- 3
- -3
Answer
(4) -3
Solution
infinitely many solutions = 0 and 1 = 2 = 3 = 0
= vmatrix 1 & 4 & -1 \ 7 & 9 & \ 5 & 1 & 2 vmatrix = (18 - ) - 4(14 - 5 ) - (7 - 45) = 19
= 0 = 0
1 = vmatrix & 4 & -1 \ -3 & 9 & 0 \ -1 & 1 & 2 vmatrix = 18 + 24 - 6 = 18 + 18
1 = 0 = -1 (then 2 = 3 = 0 also)
2 + 3 = 0 - 3 = -3
Answer: (4)