If + i and + i are the roots of x2 - (3 - 2i)x - (2i - 2) = 0, i = -1, then + is equal to:
- 2
- -6
- 6
- -2
Answer
(1) 2
Solution
Discriminant: D = (3 - 2i)2 + 4(2i - 2)
= 9 - 12i - 4 + 8i - 8 = -3 - 4i
(1 - 2i)2 = 1 - 4i - 4 = -3 - 4i
D = (1 - 2i)
x = (3 - 2i) (1 - 2i)2
x = 2 - 2i or x = 1
Taking + i = 2 - 2i and + i = 1 + 0i:
= 2, = -2, = 1, = 0
+ = 2(1) + (-2)(0) = 2
(The value is the same if the two roots are interchanged.)
Answer: (1)