The sum of all possible values of [0, 2 ], for which the system of equations : x 3 -8y-12z=0 x 2 +3y+3z=0 x+y+3z=0 has a non-trivial solution, is equal to :
- 2
- 3
- 4
Answer
(4) 4
Solution
For a non-trivial solution, the determinant of the coefficients must be zero:
vmatrix 3 & -8 & -12\ 2 & 3 & 3\ 1 & 1 & 3 vmatrix = 0
3 (9 - 3) + 8(3 2 - 3) - 12( 2 - 3) = 0
6 3 + 12 2 + 12 = 0
3 + 2 2 + 2 = 0
Putting c = : (4c3 - 3c ) + 2 (2c2 - 1 ) + 2 = 0
4c3 + 4c2 - 3c = 0 c(2c - 1)(2c + 3) = 0
So = 0 or = 12 ( = - 32 is not possible), and in [0, 2 ] this gives = 2, 3 2, 3, 5 3.
Sum = 2 + 2 = 4
Answer: (4)